I believe ww was way off and d3rr has it correct.

I'm still a newb, but I understand it more like friendship circles. You can break ties with someone and still both share friends. But if your friends find out what you're up to, like childporn, then they will tell their friends too and so on. I don't know how these white and black lists are shared.

Federated sites are free to be good bad and ugly using the same protocols, but they are not necessarily connected.

That's my take away, without actually delving.