I think what scares religious people about mental illness is the experiences of it are so much more intense than religion itself.  Both positive and negative.  It doesn’t matter if you are trying to pray your way out of it or are supine shaking your fist at God, the experience itself is intense and takes you the same places either way.  Religion likes to insert itself into everything trying to be front and center like a narcissistic teen, “it’s all about me“.  But mental illness overpowers it.  So much so that the only way religion puts it self back front and center is by rebranding mental illness as some sort of “spiritual warfare”.  Of course the treatment is just more prayer which results in a death spiral, priming yourself for some kind of experience of God which never comes (or when it does it’s really mania).  Drinking salt water my friend.