PNWReader, who recently paid me the (highly undeserved) complement of making Jason Statham his avatar for me, did not find see what all the fuss was about in my discussing what religions are "Christian" or not. For him, "expressed religious veneration for Jesus Christ" seemed sufficient. He wondered who could have the legitimate claim to be making such decisions; it seemed it was just about self-affirmation and power. And he also wondered what difference it made.
Since I do not know PNWReader personally, I cannot say whether the issue I was discussing is unimportant to him because he has no interest in it, or because he has had bad experience with religious debates, or if he has a general philosophical aversion to strong definitions.
Well, without launching into a dissertation --yes, I know. Thank God!-- I will say that words need to have definitions because otherwise language cannot grasp or communicate ideas and because ideas have consequences.
Let's just take the two groups I was talking about: Mormons and Cathars. Both claim to be Christian. But imagine what kind of church and what kind of world would be promoted by each group, based on their ideas, based on the content of what the title Christian meant to them. Or who the person was whom they named as "Jesus Christ". What, besides a bare name, gives them common ground in actual content and therefore meaning to their claim?
BTW, it would be hard to deny that both synchronically and diachronically, at least 95% of the Christians in the world hold to the foundational interconnected doctrines of Jesus as the God-Man, and of God as the Three-in-One, the Trinity.
Are the Jews for Jesus Jews?
If you extrapolate to other fields, even if there is no a priori way to decide who has what kind of standing in a debate and the outcome will always be contested anyway-- and this is the case with almost every item of human interest and discussion --, is it still not important to attempt to give definite meaning to words such as "marriage", "natural", "human person", "citizen", "rights", "man*", "God", etc.?
Essential to any definition of any kind is exclusion.
*Is Chaz Bono a man?