We're going to look very stupid in the morning if we keep trumpeting this soundbite. For the record, that is not the context in which Murtha said this:
"Our troops have become the enemy"
He was referring to the way he felt they were being shafted by the government upon their return home.
He meant it more broadly than you suggest. He meant it in the same way that liberals from Kerry to Pelosi have always meant it: our troops are hated by the left and are considered by the left to be the chief instrument of evil in the world.
Murtha merely declared his solidarity with the left on this vile point.
I believe his point, was that our US Troops have become the enemy to all of the Iraqi people.