Due to the heat and the fact that these are closed to everything so all your sweat leaks into them, I think there are some military arguments for not wearing them. I remember the story in my newspaper that when introducing the suit to the press with great pride the soldier demonstrating it fainted due to the heat and the lights and in the room. And that is only on a demonstration, not even in the heat of Iraq and the heat of battle. Story
here and
here. If that were to happen in Iraq, the US army would progress, say, one meter per day? :D