Actually, soldiers are taught that obeying an illegal order is itself illegal, and they learn roughly were the line is. While the media likes to make a bigger stink out of the cases where people forget what they learned than might be needed, it is actually pretty damn rare for western infantrymen to do something like kill civilians without provocation.

It has to do with that thing called being a professional army.

Cops, no offense to anyone here, are statistically MUCH more likely to exceed thier authority. Look at it this way- excessive force and corruption investigations are pretty common in civilian law enforcement agencies, and are known to happen every day. We've got what, a million sworn LEOs in the US, including park wardens. (We'll leave the TSA out of this, both for numbers and rates of violation.)

We've got the better part of a million US and NATO troops in Afganistan and Iraq, and so long as it is only a small arms issue, attrocities against civilians happen at a much lower rate, say every week. And I don't mean someone shoving a civilian during crowd control or shooting a dog that is trying to attack him, I mean unwarrented killings of civilians. (Again, I don't include people who were in the middle or were hit by something that missed and continued down range, but I also don't count that for police.)

I'm not saying it doesn't happen. I'm also not saying that the military makes a good police force. But you seem to be impling that US troops wind up soldiers who obey blindly. And that's about as far from the truth as can be. A sane trooper's first instinct is to protect himself and his buddies, but after that they won't shoot unless provoked.

And anyone who is no longer in possession of his or her mental and ethical facalties should be off the line, and failure to do so by NCOs and officers should be and is investigated and punished, if for no other reason than someone who's no longer tightly wrapped is actually more dangerous to his unit than he is to civilians.