@Saikatd yes they should be free to do so as well too. I don't follow HP as much as I do starwars but I'm still free to interact with HP members or join as well or even comment on posts on places like reddit. AFK I have friends as well engaged in both Fandoms.
Yes there are certain groups that are exclusive but it could be because of online/offline hate and abuse. These exists in non virtual life as well.
First is to provide a safe place to interact and slowly the change starts.