This is a pretty standard critique of MMOs, as they all focus on herding the players through a set of predefined content and none of them allow player input to a satisfactory degree. Most barely even try. One of the best MMOs for a tolerant-to-roleplay community is City of Heroes/Villains. You're still all about the fighting evil (or good), but the roleplay servers have a higher proportion of people willing to put up with your desire to read some backstory or refusal to fight a specific type of villain for roleplaying reasons. But really, MMOs are pretty shallow RP experiences no matter what you do. You could play traditional off-line RPGs. I hear Mass Effect is pretty fun.