There is one point in things like that.
Ok, you're fighting the bad guy.
If you are as bad as the bad guy, who's the bad guy?
Come on, the US is being filmed while shooting wounded prisoners on the floor, etc etc. i.e. Jailstuff.
Just look up from your pond and imagine the outside view on this.
You saw the film, I hope. The U.S. soldier simply popped a leftover-from-yesterday-flat-on-the-floor-wounded guy with his assault weapon.
So, how do yo think it looks to an outsider.
Scholzie is right IMHO, - this is NOT easily excusable. This is in itself an absolute war crime.