Film is an outlet for the appetites we're unable to express in real life, a feeding ground for our passions where we can glut ourselves in the safe knowledge that it harms no-one. Isn't it better to experience our violence and horror vicariously through film, than practise it in reality?
Online information is extremely useful, but scepticism is always required: especially with screen-grabs.
Americans have always had guns. Something else has changed in the social equation. I believe it has to do with the need to be famous, the willingness of some sick people to go to the most horrific lengths to achieve that, and the role the media play.