Well i could answer that in a very long reply, but honestly i'm to lazy, so here's the ultra short version. The reason why people go carry and shoot people (or do other unwanted things)isn't traced back to one source. It's about a balance of the harmfull and the protective elements in somebody's life. Where this balance point really depends on the person and there are many many protective and harfulling elements out there.

A person may have a really crappy life, but there faith might just balance it all to keep him happy or atleast happy enough not shoot people. But the opposite is possible too, when a personal has a good life, but has a serious negative element in his/her life that puts that person in unbalance the hole thing. Generally there are many negative elements in somebody's life to unbalance him.