@freyal

I think the point is tagging someone through the LFD tool because they are on a separate realm and you'd like to run random dungeons with them again through the dungeon finder. I could see tagging people in battlegrounds, also; if I'm interpreting this correctly, you're just trying to improve the odds of finding friendly people in random instances.

As far as "breaking the invisible walls", RealID is far more of a threat to that than tagging random cross-server people as "good to run with". Auction house collusion, world PvP antics, griefing, guild drama... not hard to do when you can talk to the other faction.

I don't really see how the LFD tool breaks realm togetherness. Although, to be honest, I'm not really sure I know what "realm togetherness" is... ? It sounds like you're using it in the context of joining a guild, and that's great if you're not in a guild and really want to be... but I'm somehow not convinced that guild membership is really a burning desire for many players: you join a guild because it's what everyone else is doing, you get random invites until you capitulate, you form your own guild so you have extra bank space and other players leave you alone, or your real life friends have a guild and it would be weird NOT to join.

To me, the very fact that Blizzard is implementing a ton of perks to join and stay in a guild suggests that active guild membership is not really a priority for the majority of players. If you have to entice people to do it, it sounds like people aren't interested in doing it in the first place.