You see its a nice idea but did anyone actually think about it? Is there even any actual way to break the geneva convention in Call of Duty multiplayer? As far as I'm aware, no there isn't.
In standard COD multiplayer there are no non-combatants, no way to surrender or be incapacitated (barring death in combat) and no way to take prisoners, and the weapons used are compliant.
In the two COD games I've played single player the people you fight (as with most armed conflict in the modern era) is asymmetrical and the people you are fighting don't follow the geneva convention but I believe the soldiers you play as do.