Well one measure of changing attitudes is that right-wing talk jocks like Rush Limbaugh and Shann Hannity have loss considerable audience in the past two years. Another is that Democratic candidates have raised far more money than the Republicans. Indeed, Republicans are quite alarmed at how poorly fund raising is going. And demographics are favoring Democrats- the older generation of conservative whites are dying off- being replaced by young immigrants who clearly favor Democrat policies. Look at the excitement and support Obama has generated among young people. The last time I saw anything like this was Bobby Kennedy in 1968.
As for violence- there have always been violent people, but technology- compact automatic weapons have made it possible for them to kill far more people now. Imagine if Seung-Hu had only a conventional pistol there and had to stop to reload after six shots. He could have been easily subdued. There is just no reason a private citizen should need a automatic assault pistol and I think the majority of Americans would support their ban. Yes, some would still be available via the black market but there would be a whole lot less than there is now when you can buy one at any gun show.