This doesn't raise the sanity waterline at all.
Yes it does. I think you need to read it again a couple of times and maybe a few OvercomingBias posts.
Unless the person is part of a very dangerous Jim Jones style of religion, what's the point?
It makes no difference to the point whether the religion is dangerous, admirable or even the literally correct and the path to eternal bliss. Thoughts about tribal affiliations typically matter more than abstract reasoning when it comes to this kind of belief.
Your statements have the implied premise that having true beliefs raises the sanity line even if the process of reaching those beliefs is not correlated with the correctness of the beliefs.
I prefer "raising the sanity line" to refer to increased usage of processes correlated with creating correct beliefs. Your hostile reaction to this understanding doesn't exactly advance the ball on figuring out how to actually achieve either goal.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.