Argh... Freeza, you're missing the point. There are THREE modes of play in the game: Single Player Campaign, Co-Op Campaign and Multiplayer.
When I say Co-op, I'm talking about a mission mode that requires at least two players to complete.
In Multiplayer games (e.g. Deathmatch, Space Race, Land Rush, etc.), any of the players can do whatever they like. They can ally themselves, they can stab eachother in the back, whatever people do in games like that. It's a given.
But the Co-op mode is a campaign mode in which you need at least two players to get through the missions. A single player just wouldn't be able to do it. There would probably be one or two Co-Op campaigns and not much more.
Then there's the single player mode which currently has 4 campaings for the player to complete. (well, it will when they're done)
Of course, I don't know if I want to do the co-op mode. I need to talk to the other guys before that's decided upon.