A community can add you to its friends' list just as a user can add you to their friends' list. Along with that you don't have to add anyone to your friends list, just as you don't have to add a community to your friends list. You can remove yourself or I can remove you. I think anyway that you have to join the community yourself before you can post.

I added people who seemed to be interested in aviation or flying. If your truely not interested fell free to unsubscribe.