Well... I'm not a mental health professional. So I can't offer anything in the way of a diagnosis that might be applicable to the members you describe. What this sounds like to me is that, perhaps, it might fall under the "heading" of schizophrenia? There's a forum, here on PC, dedicated to Schizophrenia & Psychosis. Perhaps you might take a look through some of the postings in that forum & see if there is anything there that is of help in terms of gaining some perspective regarding what you're dealing with. Here's a link to that forum:

https://forums.psychcentral.com/schi...and-psychosis/

My personal non-professional opinion would be that how you are handling the members you're concerned about is fine. I wouldn't forcibly segregate them of course. However offering them their own forum, it seems to me, is an appropriate way to proceed. I don't believe there is really an issue, or concern, here with regard to enabling.

You wrote that what you'd like to do is to not provide these members with this special forum, to end it. But you don't want to cause the members who use this special forum any issues. I personally think the question here is more one of what do you need to do in order to manage your website. You have these members who believe they are actually in contact with bigfoot. Can they be integrated into the rest of your website without undue disruption? If not, & if you don't want to apply whatever restrictions your website has with regard to such things as arguing etc., then I think perhaps the path of least resistance, so to speak, may be to simply continue to provide them with their own forum as you have been doing. Does that make sense?

Anyway... thanks for bringing your concern here to PC. The problem you describe is certainly an interesting one. My best wishes to you...