Was Barnes really a 'bad person'?
I think he just felt like he needed to do to accomplish the mission, or whatever other cliche there was.
Remember when the two guys are blown up in the bunker by a booby trap. He's sitting there looking sad and reflecting and Sheen catches him doing so. He offers the LT to play a game of cards with them. And I would have been pissed if the commanding officer gave wrong coordinates getting 2 men killed and 2 wounded.