I think in most cases this isn't true (who cares how niche your hobbies or style are), but when it comes to internet mental health discussion communities there definitely is a double edged sword IMO. Depends on the community and person, but I suspect you're right in the case of e.g. finding others who are depressed, there's a lot of overshoot in the reaction to stigma in some of these groups, to the point it encourages giving into some pretty bad lifestyle loops.