I still say this is about trying to help make the best possible experience in the game, and the truth is grouping with a personality that you just hate can kill this experience for you. MMO's are all about the community. If your experience with the "community" (which is really just the players you run into in game, by pure luck a this point in time) ends up being bad, then you most likely won't keep playing the game, or you'll have bad things to say about the community, which give the game a bad rap, and over time can kill it. So how do you solve that problem? You present each player with the "community" (again in an mmo the community is really a small pool of players you happen to run into) that they will enjoy the most to give a higher chance (again it's all about odds) that they will have an enjoyable time.
And that's the original point of the thread. Only my solution is to eliminate the "pure luck" element you state of running into players you can work with by implementing low population invite-only servers (but anyone can purchase their own server to start). Your solution is to implement more thorough matchmaking mechanics. I think both methods could work.