I would say this continues to be "I have a definition and I want to stretch it to fit because I like calling those people 'cultists'". It sounds like I'll be "ostracized" exactly the same if I leave HN, if we stretch "ostracization" to include "well, I used to talk to those people in that forum but now I don't, so I'm being 'ostracized'".

I wasn't in a "cult" because I was once, a long time ago, in an Ultima fan community, but then was "ostracized" because I left. I just left. There were no consequences beyond the fact that I left. The problem with cults is that they don't "ostracize" you by virtue of failing to chase you down if you leave, they are cults because they do chase you down if you leave. Again, I have a hard time believing in "cults" when the "cult" in question literally doesn't even notice you. That's not a cult.