It's so comforting to believe in a golden age...
But if you look just at murder rates, according to the FBI's statistics, the rate per 100,000 averaged 4.9 between 1950 and 1959. It went up a bunch from 1960 to 1980, then began to go down again. Between 2000 and 2007, the homicide rate averaged 5.7, and in 2010 it averaged 4.8. (This is just what I turned up in a quick search -- dunno what happened in '08 and '09, but my impression is that it's consistent with that trend.)
So overall, if we were in some golden age of low violent crime in the '50's... we're there again now. And if I have to say this -- mass murders of the kind people get so wound up about now are, and always have been, a tiny
percentage of the total. What has changed is the news cycle: we hear about them instantly from an increasingly sensationalistic and fear-mongering press, and this makes them seem much more common than they are.
Whether it's blaming guns, blaming the mentally ill, or blaming the media, our obsession with finding a single, "master-molecule" explanation -- a nice, simple, comforting fix to believe in -- prevents us from being open to the complexity of the real world and real people. It's too bad, because I doubt that there's any one-size-fits-all explanation for why people resort to violence.