Well... what if the players try to save the NPC?
If you say I do what I want with my NPCs so one NPC just kills another with NO possibility of the PCs stopping it then it kind of takes the fun out of trying.
Except that's not at all what I'm saying. At all.
What I'm saying is simply that if the MC/GM decides an NPC gets shot through the heart in *World games, he's dead, no roll no nothing, because that's what the fiction says (unless the fiction indeed says otherwise, say the victim is a zombie). Likewise, a player whose character is going to stab someone in the back without being noticed doesn't have to roll for that. There's no conflict there, he just does it. That's how *World games work.
That's what the confines of the fiction are. In a WWII game, my players can't jump a hundred yards on to the top of the roof where the sniper sits, they're not superhuman. That doesn't mean the sniper is just going to kill all of them without them being able to do anything about it.
If a player stands next to killer A, who is about to shoot helpless person B and the player pushes the gun, cool, roll for it. None of that means that if the bullet had hit B's heart, it would not have been deadly.
Those are two different questions. Just because I can kill my NPCs through fiction doesn't mean I will. I did not say I'm going to kill any random NPC I want and prevent my players from doing anything about it after all.
That applies to other system in the sense that it would be insanely silly to say "He cuts his throat and *rolls 1d4+2* does 3 damage. Do you stop him or do you give him the additional 5-10 rounds he needs with his dagger to kill this NPC?" If an NPC's throat is cut, it is cut.
Again, that does not mean the players couldn't do anything about it by default. There may however be situations where the players can't do much, or indeed, anything. A drive-by shooting like
bradscott wants? Not a lot the players can do. Which kind of is the point of real life drive-by shootings.
Again it depends on the fiction. If someone's starting to shoot behind the NPCs back, they're probably hosed and rightfully so.
Of course the GM needs to be a bit careful about how he employs those situations where player agency is diminished, but that's 1) another issue and 2) entirely legitimate for a con game starting in the middle of the action.
I disagree, but I'm not interested in a general discussion about rolling behind the screen or not. You can do what you want after all.
What I said is: in this particular situation, it rubs me the wrong way and as a GM you're running the danger of disengaging a number of your players right from the word go without any appreciable benefit.