I never thought about how it can be confrontational with the overlord. That never came up in the games I've played.
I wonder of all the tabletop RPG's I've played inoculated me against that. I'm already used to this sort of 1 vs many gameplay.
I've known confrontational players, but the hero/OL dynamic remains one of my favorite parts about Descent. If I want to play a cooperative game, there are better choices- like Pandemic or Robinson Crusoe.