Well the U.S. now has an all volunteer military so I suppose a few people might enlist just to get the chance to kill somebody. I don't think that's common though. Mostly they are carefully trained to do exactly what they are told and don't stay long if the training doesn't take hold.
I don't forgive the U.S. government for these attrocities but I'm inclined to give the foot soldier the benefit of the doubt. Maybe I'm not seeing the reality.