This is, actually, a good place to acknowledge the issue of context which comes up in numerous shooters.
Playing Left 4 Dead not too long ago, I gunned down six police officers in a single campaign. Granted, they were all infected and zombies, but shit; that still makes me (within the game) a cop-killer, and wouldn't Jack Thompson and Hillary Clinton and Fox News have a field day with that?[footnote]This is why, incidentally, there are no riot-police Uncommon Infected in the German release of Left 4 Dead 2. They didn't take kindly to the idea that the survivors would have to fight peacekeeping officers.[/footnote]
I sometimes also wonder if the game would feel any different if we were on the verge of a medical breakthrough, and all these berserking commons could be cured, if they were captured and treated in time. It remains an issue that when zombies are no longer magically-[footnote]...or atomically-...[/footnote]raised undead, but alive and infected, which means they are still human. Even if their brains have been fried by some kind of super-rabies or mad-human prion, they would still have rights according to every civilization known.
So, one of the easiest ways to raise the questions that come up with school shooting would be to create a Left 4 Dead campaign that includes wading through a school as part of the journey to safety and rescue. Zombies in school uniforms and faculty attire would hit the point home: The players are still shooting up a school, albeit, one in which not too much academic learning is going on anymore.
238U.