What makes communities special is that a group of people share the same interest and you feel a sort of a bond there. You can talk about things and people get it, unlike the general population. Besides, it can be weird stuff that most people won't relate to. I think it's really important that people have to join communities to participate in them, even if it's something as trivial as clicking a join button. Otherwise it's not really a community and you're broadcasting your random niche interests to everyone.