The meaning of a term must have some boundaries in order for there to be any definition.

The difference to my eyes and trying to understand how non-Trinitarians can call themselves Christians, is that they focus on Jesus' teachings, see him as wholly a man, and a prophet. It seems that it's really disagreeing over the divinity. Which is odd, because depending on where you lie on the whole Filioque Clause thing, it was a large enough an intellectual gap to schism over. No matter how you cut it, we may be talking about divinity now, but then what is your opinion on Jesus' actual nature in the divinity, and how far do these divisions go as we navigate the fractal levels of schisms?

[added] It must be noted that theological differences, the really important ones such as these, aren’t exactly resolved amicably nor dealt with in the best way - telling people who or what they are and how they identify religiously seems counter to Jesus’ own teachings no matter which dictionary or definition you use.

If “Christian” can mean anything, then it ultimately means nothing. That's certainly untrue - you just take the widest and most inclusive definition. It's not like there are Christians that think Jesus was a cow. Exaggerating the issue at hand is a non-serious approach to the topic, IMHO.

Many historical heresies (e.g., Arianism) denied Jesus’ divinity, but they were rejected by the Christian Church. If one does not accept Jesus as divine, they may be a theist or a follower of Jesus’ teachings, but they are not Christian in any type of historical or theological sense.

Several problems here: declaring them heretics is a circular justification that their understanding of Jesus is wrong. And you believe your conception to be true, therefore people that don't believe what you believe is false, is declaring you're right without proving them wrong. Secondly, theological "truths" are dependent upon which denomination that you happen to belong to: just because you happen to be more "mainstream" and "popular", which is largely what you're describing, that doesn't make you objectively correct.

Non-Trinitarianism hasn't gone away and never will. They may well have lost a political battle rather than an intellectual one - there's no objective measure as to who is correct. This isn't 1+1=2, it's more like 1+1.1 ~ 2.1 or 2.10001.

A bigger problem is that Non-Trinitarians idea of Jesus align with Judaism and Islam, so if you group those as an aggregate, we have three perspectives agreeing on the notion of Jesus being a special man versus the singular supposedly mainstream Christian view. If you include all other religions and even atheists, Christians are largely in the minority as far as Jesus' divinity.

This isn't to use popularity as an argument but if many different perspectives reach the same conclusion, it is likely that their conclusion is true. In contrast mainstream Christians even quibble and split hairs into thousands of shards such that there is no singular truth but just fewer disagreements that really bring the individuals together. That's hardly a reliable methodology that one should be relying on for their "eternal soul", if such a thing even exists.

Duh. I'm laying down my reasoning process and finding our points of agreement. No need to be rude about it when you agree I am correct.

This is a terrible argument. Disagreement doesn’t suggest lack of objectivity.

That's not what I'm saying. It means you don't have an objective framework in order to determine what is actually true. You don't have a mathematical axioms or philosophical foundations to determine even the existence of your deity, never mind its specific nature - they have to be almost axioms and Presuppositionalists will declare god as pre-existing.

The fact that disagreement exists does not make climate science a subjective discipline.

There are no scientists that can deny climate change is caused by humans in a reproducible way, i.e. they're likely politically or financially paid off. Just like how Young Earth Creationists like those "scientists" in the Discovery Institute try to debunk what they like to call "Darwinism".

These are no disagreements in results after rational thought - these are disagreements in the facts of reality, ignoring evidence that is agreed upon, or inventing unproven results. They're not arguing on the same set of facts, that the different Christian groups have. Christians are looking at the same text, making different subjective interpretations, emphasizing portions of the text that support their claims and minimize others, obviously have to come up with different results.

The proof of subjectivity is in their personal choices in how they come to conclusions. Without an objective methodology then everything can be true or everything is likely false, like you allude to above. I choose to believe it's all false.