Well the level of alliances also doesn't have to be consistent. Obviously some will get along very well, others will barely be able to stand each other's presence. So even in teams where there is no chance of defection, they don't have to get along at all. So yeah, plenty of room for all kinds of things. It just makes interacting difficult if the character just doesn't want to get involved. It defeats the purpose of a group game to have a bunch of loners, or at least that's how it seems to me.