Sorry to butt in here, but I feel like Chris might be missing something important here. That part about the 'where are the PCs in this story'? For AW, they should probably be right up at the top of that Dramatis Personae list. Your NPCs sound so complex that you had to put a (NPC) tag up on there so the casual observer could tell the difference between PCs and NPCs. Are you looking at your NPCs through crosshairs? AW really wants you to make NPCs expendable, with obvious motivations- they follow their parts. That's mechanics on the MCs end.
You mentioned you built some triangles between PCs and NPCs- were you enough of a fan of Monster Truck that he felt he had a stake in the situation, something to lose if he just started shooting? AW wants the Dramatis Personae to be the PCs, not the NPCs, specifically because of this tendency to git to the shootin'. If every NPC comes across as a whiny, complex bundle of emotions that needs to be carefully unpacked in order to have a fun game, there's a distinct kind of gamer that is going to unpack their carefully-designed brain with a full clip of armor-piercing rounds.
The players end up driving a LOT of the action in AW- what was Monster Truck's shtick besides 'shoot everything in sight'? Was his hard highlighted, session after session? If Monster Truck's the 'I kill things to take their stuff so I can kill bigger things' type, I'd just highlight his hot and his weird until he figured out that he doesn't get new powerful moves that way, he just gets a big pile of trash to sort out. It might've been valuable before it got ran over with a monster truck, but now, it's trash.
If the other players weren't cool with pulling the game in two different directions (some players want to have complex conflicts involving multiple factions of NPCs, Monster Truck wants to git to the shootin'), then you might just have an interpersonal problem rather than a mechanics problem. I'm pretty sure I wouldn't want to play with a player who insists on having a character with 'no morals'... in any game. If the other characters weren't cool with it but the players were, why wouldn't the other players roll to interfere until he messed it up real bad, which happens eventually? Even if this guy is some hot-shit +3 hard grizzled vet, a -2 knocks it down to a +1 pretty quickly.
In short, I feel like there are plenty of mechanics in AW which should have prevented this scene from ever getting to that point.
Orpheus, your problems are a lot easier. If your buddy wants combat, AW has rules for it. They're not the pull-out-the-battlemat, shift-some-minis-around-and-argue-about-cover kind of rules, but they cover it pretty well, and if he wants it to happen, oh boy will it happen. If he likes it, great. If not, well, thanks for giving it a shot, buddy. Then you either go back to whatever RPG you all enjoyed playing, you tell your buddy you'll let him know the next time you start up another RPG he likes or is willing to try, or you force him to play AW until he drives a monster truck through your game. ;)