Beside privilege (which I'm taking to mean, "part of the locally dominant group") and not being used to opposition, there's probably also a reason to be found in absolute phrasing being a form of identity assertion. Inversely, relativizing or limiting language would be a form of self-denial. You can do it with effort but judging from its general lack in many areas it's not a natural mode of speaking.

One Christian on that site has said publicly that to qualify his language in any way is to deny his faith. I had hoped he was unusual in being that extreme, but I'm starting to think he's unusual not in that but in admitting it. There are several users who routinely assert their beliefs as truth -- and get away with it because of majority privilege, including moderators who agree with them. (A new moderator was recently appointed who is more sensitive to these matters. Time will tell if he makes enough of a difference. It's not like any moderator really likes to confront a fellow moderator, after all.)

I'm sure you've heard of the psychological thing where someone who's doubtful about an important belief of theirs will try to convert others to it? And the one where people presented with belief-contradicting evidence will see it as an attack and double down on the belief instead of giving it up?

I hadn't thought about that, but yeah, that makes sense. This is why these conversations can't (usefully) ever be about "what I believe"; there be minefields. It's only possible for it to work if people can step back from that -- but for many people, it's the (perceived) opportunity to express their beliefs that attracts them in the first place.

Thank you for sharing your thoughts.