I'm surprised that no-one has mentioned the possible effect that things such as TV and computer/video games have on children as they're growing up.
Way back when I was young the most violent thing I saw on TV was 'The Lone Ranger'. And there was no such thing as the internet and video games.

When my son was young 'He-man and the masters of the universe' was just becoming popular. Skeletor gave me the creeps so I refused to let my son watch it. Though it seemed every other 4-year old at his nursery watched it. (So I did eventually relent, though very reluctantly.)

Censorship at the cinema has been relaxed to such an extent that 12 year-olds can see stuff which 40, possibly less, years ago would have been rated 18 years. Plus films are now on TV 24/7. Back then you only saw a film on TV at Christmas and Easter.

Nowadays there's all the video games, some of which seem to consists of continual shooting of people. What sort of message does that send out, for goodness' sake? And even if those kind are labelled 18, you can bet that children much younger than that are playing them.

People in the UK are saying that gun control is not the answer because since gun possession here came under quite severe restrictions gun crime has actually increased, though I have no statistics to prove or disprove this. . The new laws were brought in following a massacre at a school in Dunblane (Scotland) in 1996. The gunman, Thomas Hamilton, had four handguns, which he was licensed to hold.
However much you regulate gun control there will always be the madman who somehow manages to get arms and ammunition and kill indiscriminately. Though there's nothing to stop the government making it harder for them.