Not true IME. I run the worlds largest Yahoo group for mentalists (the branch of magic devoted to simulated mind reading - Derren Brown stuff in a nutshell). It has 350+ members worldwide.
Access isnt unlimited to be fair, but prospective members have to satisfy me of a genuine interest in the subject before they can join. It works out OK, takes very little time. I currently only have one member whose posts are 'moderated' because he became abusive to another member.