Last line is exactly correct, most of the psychos come from bad parenting. Legislating parenting somehow would be effing great, but mostly a pipe dream.
I think the only way you're going to educate the general public about guns, safety, operation, etc is some form of forced conscription where every person who comes of age is forced to take at least a course, if not spend a year working for the damn military (doesn't sweden or someone do this?) I don't see that sort of thing going over terribly well, though..
Banning social media is probably the best, most effective possible course of action, IMO. And force everyone back to having anonymity on the internet. If i don't KNOW you're a gay, black, trans, gun-loving, hickster, then I don't really have any motivation to taunt you, bully you, dox you, or fuck up your whole damn school.