The person I know locally who's getting into this seems to be heading for a schizophrenic breakdown.

I've had two friends in the past who went the same way, passing through fringe beliefs on the way to horrible suicides - one was involved in Theosophy and poisoned himself with phenol, the other went through Tantric Buddhism before starving himself to death in a derelict building. I don't blame the Buddhists, their support obviously wasn't enough but it's hard to imagine what could have been. The Theosophists were outright murderers, egging the guy on into deeper and deeper craziness and grandiose detachment from reality.

My guess is the flat earthers are in between - it's a belief system guaranteed to draw in a lot of people with profound mental health problems, but with no provision whatever for helping them.