The thing about MMO is I have absolutely zero interest in interacting with other players online. I don't want to have to rely on somebody to complete a crucial quest, nor do I want somebody else to feel reliant upon me. Having a crew of NPCs that I control (like Dragon Age) is fine, but other than that, no thanks.
The only time I ever played on line was Star Wars Battlefront II, and the only thing I did was fly a fighter. I didn't do anything dickish like shoot down my own teammates, but I certainly didn't give a crap when they died. Eventually I quit playing because I got sick of the morons who would wait by the spawn points and kill you before you could get to a ship. Douchebags.