Actually when they've interveiwed school shooters and such they have found the opposite to be true, these kids come from very permissive homes where the parents never raised a hand to them no matter what they did wrong. Like Ethan Crumbley's parents who let him get away with anything and always looked the other way no matter how many animals he "experimented" on.

Kids need discipline and sometimes physical punishment is the only sure way to get their attention and make them see that their actions do have terrible consequences.