> when I was in the Marine Corps, one of my drill instructors said something to the effect of "You know why I joined the Marine Corps? Because it's one of the only jobs where you can legally kill a [expletive]."

How confident are you that he actually earnestly meant this? I've heard DIs / SOI instructors say things like that on several occasions, but it was all pretty clearly within the context of trying to be "motivating"....they didn't come across as actually psychotic.