You know, in WoW you can have a cross server friends AND ignore list if you want. So, technically it promotes community because you can actually make friends from other servers you meet while doing LFG if you choose. You can then add them to a friends list and talk to them / group with them in game. If you come across a d-bag while in LFG you can put them on ignore and never meet them again. This pretty much works the same as a 'blacklist', though so does ignoring someone from your own server.