Loadingxml's article can be found here. It will obviously be extensively referenced in this page so it's recommended reading if you haven't already.
I think this section contains mistakes endemic to a lot of Muslim attempts at explaining the Trinity that I see, so I don't hold it as a personal fault; nevertheless, it is still wrong.
The first problem that presents itself is his choice of analogies in substitute of actual arguments (for which he provides counter-arguments). Generally it is held that the Trinity can't be explained by analogy since it is by its divine nature unique. An analogy might help explain the concept, such as St. Patrick's explanation of the shamrock, but can't be considered to be a one-to-one explanation or comparison. Such a comparison necessarily does not exist since what you would be trying to compare is some temporal physical object with the eternal divine nature.
Personally, I think the best one is the example of man. A man has both an immaterial and material component, a soul and a body, if you want (for the analogy it's not relevant the names we give to them or if you think there's more than one immaterial part). Now your soul is you in this case, and your body also is you, and yet clearly taking away one would leave the other destitute of life as we recognise it. Without the soul the body would be a dead shell without consciousness and without the body the soul has no material presence, it cannot affect anything about it. So, the body and the soul are you (the man) but they clearly can't be the same thing.
But yet, and this can't be overstressed, man is not God, and the analogue only serves to show that things can both be one thing without being one another; it isn't supposed to be a direct comparison to God.
I will say I like the rebuttals to some of the "explanations" of the Trinity (the Sun rays, the multiplication examples) because I think those analogies are faulty already, so I don't have a problem with those specific arguments so much as his decision to assume these are cogent arguments in favour of the Trinity in the first place when they are not.
In the quoted section of the dialogue, the author is trying to argue his point:
Then I replied, "Reverting to the Scriptures, I shall endeavour to persuade you, that He who is said to have appeared to Abraham, and to Jacob, and to Moses, and who is called God, is distinct from Him who made all things,—numerically, I mean, not [distinct] in will. For I affirm that He has never at any time done anything which He who made the world—above whom there is no other God—has not wished Him both to do and to engage Himself with."
Which is rather the opposite of what loadingxml is trying to claim, that somehow Justin Martyr was trying to say that the Son was subject to the Father. In fact the claims mostly revolve around the difference between the Father and the Holy Spirit rather than the Son, and even in the original quotation xml supposes Christ is referred to by
...another God and Lord subject to the Maker of all things... [my emphasis]
(That is, another God and Lord, not another prophet) Which would directly contradict what xml is going for (that the early Christians were not trinitarians and didn't think Christ was [in this case, a] God).
As quoted above, the author of the dialogue specifically states that this "other God" (the Holy Spirit) is:
distinct from Him who made all things,—numerically, I mean, not [distinct] in will.
So in other words, distinct in person or number, but not in essence or will. In twice different words, exactly what Christians teach.
I may read the full dialogue and add to this section in time.
What follows is some quoting of scripture that superficially seems to support subordinationism, it's pretty weak in general. Just for example, he doesn't seem to notice in one of his own quotations is a direct refutation of his claim that trinitariansim is a non-scriptural heresy:
My Father, who has given them to me, is greater than all no one can snatch them out of my Father’s hand. I and the Father are one. [my emphasis]
"I and the Father are one" huh? I wonder what sort of doctrine that could lead to...
The rest of this section is equally weak, first there is the fallacy of this pick-and-choose attitude in regards to evidence. Some ante-Nicene Church Fathers were subordinationists, some weren't. It's useless to treat the whole of Christianity before one specific council - that xml has chosen for reasons convenient to his polemic rather than rational - as a monolith because it leads to this. His favourite heretic, Arius, was even expelled from his position in the Alexandrian church because of his teachings on the trinity, but this is ignored in favour of the argument that because they existed, the belief must have been widespread and even orthodox at the time.
This sentence I think displays xml's fundamental misunderstanding of the doctrine:
Its like they are playing with toys, lets add 2 extra Gods, because why not...
Two extra Gods weren't just added because why not, they are there because it is evident from scripture and Church tradition that they exist. The mindset that all this dogma is arbitrary and something people just came up with instead of revealed truth about the world is the fundamental misunderstanding here. I may as well ask, why is Allah one and unitary, why is not a trinity, or a quaternity? Surely 1 is just as arbitrary a number as 3, or 4, or 63? We didn't logically derive everything we know about God, and we certainly didn't make it up ourselves. Otherwise neither of us would need our scripture because we'd have it all argued out in our heads according to pure rationality.
To use an analogy - which I hope will be understood as not being a one-to-one comparison now - why does a proton have the mass it does? Why is the ratio between a proton's mass and a neutron or electron's mass the value it is? Maybe that looks totally arbitrary to us, we can't logically derive why one of those numbers is 1836:1837 instead of any other pair of integers (or if you think you can, pick some other natural constants for which you can't, it doesn't matter) but that doesn't make it not true and it's the height of arrogance to think you can outwit God, just because you don't like the number 3.
The thrust of xml's argument here is that Roman emperor Constantine I is the eleventh horn referred to in Daniel's prophecy (Chapter 7 of the book of Daniel) and has a poor enough character to be deemed the ruiner of Christianity due to his influence in the council of Nicea. The "eleventh horn" idea will be dealt with later.
One problem with this claim is that many of the evidences brought in support of this could easily be taken to mean the opposite. Take the first quotation as an example:
"Different from the earlier ones"
he [Constantine] did not formally renounce heathenism and did not receive baptism until in 337 he was laid upon the bed of death.
he ordered the execution of his conquered rival and brother-in-law Licinius, in breach of a solemn promise of mercy (324). Not satisfied with this he caused soon afterwards, from political suspicion, the death of the young Licinius, his nephew, a boy of hardly eleven years. But the worst of all is the murder of his eldest son, Crispus, in 326
He also never relinquished his position as chief priest of the pagan state religion, and his coins proclaimed his allegiance to the sun god. He delayed Christian baptism until shortly before his death
So, Constantine was different from the other emperors, we are told. How, exactly? Well he was not a Christian for most of his life, just like the previous emperors; he murdered members of his family to keep hold on power, just like previous emperors and he was brutally cruel to his subjects, just like previous emperors. You'd be forgiven for wondering how all this supports the idea that Constantine was "different from the earlier ones". It's not explained.
"speak against the Most High and oppress his holy people"
Now blaspheming Christ by putting him on the same footing as the Sun god would be a fulfilment of this prophecy, were it not for the fact that every emperor before Constantine could also be said to blaspheme Christ by persecuting his followers. Trying to stick the council of Nicea to this line is also weak since it relies on a preconception that Arianism is the truth and trinitarianism is a Nicean heresy (or whatever he'd call it).
"try to change the set times and the laws"
So what's xml saying here? Holidays we generally associate with Christianity were codified by Constantine rather than, who, Christ? Of course they were, Constantine was the emperor and in Rome the emperors decided the calendar. Before Constantine there were no emperors sympathetic to Christianity so naturally there were no officially observed Christian holidays. This is not to mention the contradiction in his own quote (once again):
It seems likely that Constantine, trying to unite the worship of the Sun with that of Christ, pushed, if he did not concoct, the observance of Christmas. [my emphasis]
So Constantine is the big-bad, who has corrupted the Word and ruined Christianity, but he didn't even come up with the idea to put Christmas on the date of the Sun god festival! Unless Consantine was playing some 4D chess here with the Roman public this just seems like a political convenience for him rather than a premeditated pagan assault on monotheism. And again, xml takes this arbitrarian view of history where these things just happened, and acts as if there weren't legions of bishops and presbyters (as in, the people who actually attended the council of Nicea) who were perfectly capable of pointing out paganism if they felt it was infecting the Truth. After all, they had already been persecuted for centuries over refusing to succumb to pagan sacrifices or rituals so why would they stop now? It just doesn't make sense unless you approach the whole situation with a preconceived mindset that Christianity was corrupted at this time and place.
This section also contains numerous mistakes, and is found here
Loadingxml states as evidence for Constantine being the eleventh horn that the first ten horns represent ten emperors who persecuted Christians. In listing the ten persecutions, he fails to realise that one of the persecutions took place under two separate emperors! The Antonine emperors, father and (adopted) son, persecuted the Christians. Under his logic, this would make Diolectian the 11th horn and Constantine the 12th!
The rest are not worth their own sections, so I shall list them
This section will unfortunately consist mostly of adding context or rebuttals to certain passages of the original article, it won't be as coherent as previous passages.
“About Jesus of Nazareth,” they replied. “He was a prophet, powerful in word and deed before God and all the people. [Luke 24:19 New International Version]
The man speaking in this verse is not God, Christ, or Luke, he is just explaining to what he believes to be a random stranger what he and his partner were talking about on the road; there's no reason to take this as any statement on the nature of Christ.
So the first "God" word was defined, which mean that the "Word" was with "The God" and the word was "God", which will end up meaning "a God was with The God" giving the fact that the other "God" word wasn't defined, in simple term, this mean there is two Gods, not one, and so this contradict with one God rule we said above.
This isn't right, he's just added in an "a God" out of nowhere. The second appearance of "God" doesn't have an article prefixed to it, because in that case in the sentence "God" wouldn't necessarily need one, it's a proper noun.
Now that "like God" isn't right, this Source and other translations translated it as "as God to Pharaoh", so you can be called "God" easily in Christianity
A simile is using the words "like" or "as" to compare two things, so swapping out the two words doesn't change the meaning, it's still clearly not literally calling Moses God. A lot of these points are seemingly just from a lack of understanding that the word "god" doesn't always have to mean the monotheistic God, in the west our cultures were historically pagan for a long time so there is an understanding that lowercase god can be used to describe something with lots of power in its domain, rather than the uppercase cosmic God. (Note I'm just using that lowercase/uppercase distinction for my own sake, I'm not claiming it was present in scripture). Arguing against this is arguing against literary convention more than anything else.
Next he claims that there is no difference in the use of "Holy" between Luke 1:35 and Mark 6:20, but his own evidence of Greek translation he provides, we can see there is. In Luke holy is modifying the noun (holy-thing), whereas in Mark it is just describing the man (just and holy). I wouldn't even regard this as a "proof" of Jesus being God (note no indefinite article in front of God there) but it just shows how even this is incorrect in his article. Either way it certainly doesn't give any evidence against it and being called a Holy Child who is the Son of God seems to pretty nicely fit in with Jesus being the Song of God and all, and I should remind you that he should really be trying to show Jesus was just a prophet, but is settling here for him simply not literally being God, but rather subordinate to him; which he has to settle for because the scripture contradicts Jesus-as-a-prophet. So which is it? either you can use scripture to argue against Jesus' divinity or you disregard scripture entirely (because it calls him the Son of God); I don't think it's fair you do both.
I am the Lord, and there is no other; apart from me there is no God.
Let them know that you, whose name is the Lord— that you alone are the Most High over all the earth.
You were shown these things so that you might know that the Lord is God; besides him there is no other.
Another misunderstanding of the Trinity. There is no God but God, that is true because the Trinity contains only one God. You can only interpret these as being against the Trinity if you come in to it already believing trinitarianism is polytheism. You have to start at the conclusion for these verses to actually mean anything in support of his argument, so it's circular reasoning.
A few other Christians and I dealt with this section in the chat, so for brevity's sake here I'll omit the arguments. I might come back and update this later, might not.
So this section is also rife with fallacies, a little easier to debunk without reference to the text though.
For one, this supposed lack of evidence for the Bible's authenticity is absurd. We have more evidence for John, Luke or Mark etc. than we do for Plato, Aristotle or Homer. If loadingxml believes Aristotle was a real person and not invented by scholars of antiquity then how can he justify this belief that the gospels were?
Next he unwittingly comes out in support of sola scriptura (GNU/Calvinism/Islam when?) without seeming to realise this is a matter of intense interdenominational debate in Christianity. Catholics absolutely do believe that scripture is not necessarily the highest authority on the gospels and I think the majority of Protestant denominations disagree (I say "I think" because you can never be too sure given the sheer number of them) with that.
Also the first quotation used here (Romans 10:17) refers to "the message", "the word" or "the saying", rather than specifically a written wod (scripture) so I don't think it's a good argument in support of the doctrine of sola scriptura even if I happen to agree with it.
I read this last bit after writing the previous paragraphs so the argument I just made comparing the gospels to ancient authors is even quoted in his own article but not addressed. Hmm.
I don't much care for the rest of the article so I shan't bother debunking any of it.
Thanks to my fellow Christians who helped in the chat, and especially thanks to the man loadingxml himself for providing such stimulating debate in the first place, and I mean that with complete sincerity. Maybe parts of this come off as rather hostile but I don't mean that way and I'll gladly revise any section he thinks is excessively offensive or unkind.
Lastly I suppose this is technically a work in progress, there are many sections I might come back and actually finish, or just edit for clarity. If I fix any mistakes then I'll put a note where there used to be one, if not in the text then definitely in the HTML comments.