Hmmm... I think friendly fire in certain games is important and possibly vital. It helps establish team consequences and emphasizes good aim. The problem though with friendly fire is it is very easy to troll with and doesn't work well with AoE style weapons as you cannot use precision shots.
I don't think it would go well in MA with so many AoE style weapons but perhaps it is less about the players and more about the map layouts causing the bottlenecks.