> it's not the rational part of your brain that going to stop you from pulling the trigger. It's a deeper
> part more "primitive" part of the brain that stops you from killing another person.

There was a C4 documentary about this: The Truth About Killing which makes interesting reading. However, I gather the studies are controversial. See for example, S.L.A. Marshall and the Ratio of Fire.

I doubt you can really tell in advance how someone would react. The idea that people can be divided into sheep, wolves and sheepdogs, in advance, is probably simplistic, and I suspect that the same person might act as sheep on one occasion and sheep dog on another (and wolf on yet another). It partly depends on the situation and on what other people are doing.