You don't get it. Part of building a community (you know, the whole idea of keeping the LFG system bound to single server) is to make sure our fellow players are aware of a bad apple. Putting someone on your ignore list helps you, but it doesn't help the next person who gets stuck with them. By making others aware of a dirtbag, you're doing your part to make sure the community is just a tiny bit better. (Of course, I do realize I'm most likely talking to a brick wall in the only person that matters is me generation)
You're not going to be able to prevent other people from queuing if you don't like them. This seems to be an argument against any kind of random dungeon finder, not just whether it is same server or cross server.