Most of the damage that kills them is to the face. Even the riot cops get a helmet. Master Chief seemed to work out well with one. You could even put a gas mask and a little fan on it.
This is what happens otherwise.

if you are lucky enough to live.
Iraq or Afgahnistan it is a nessecity of modern warware to have a ballistic foam helmet with a bulletproof glass visor. Our dirtbike racers are better equipped isn't that stupid?