You know what's really exciting about video games is you don't just interact with the game physically -- you're not just moving your hand on a joystick, but you're asked to interact with the game psychologically and emotionally as well. You're not just watching the characters on screen; you're becoming those characters.
NINA HUNTEMANN, Game Over
An MMO is the ultimate single player game. You're free to do what you want and other players provide the best background entertainment. The word grouping doesn't appear in MMORPG for a reason. It's just a lot of players online, what they do is up to them.
Waiting sometimes hours for a group to come together or a PUG that had a crazy person in it who wiped the group on purpose, or a new player still learning his class that has to be carried, or group drama.
Games have more freedom now, you can still get together with a group of friends or try a hundred guilds until you find the one that's right for you and enjoy grouping, or solo, or public groups.
But if you're talking about a game with forced grouping because it's the only way it's designed to be played, no thanks, that would feel like a step backwards to me.