I don't think there's any one thing to blame for the mass shootings. When I look at modern society as a whole, I see a lot of things that I think add to the problem. Broken homes, and broken up families. Families scattered all over, so that no local support structure exists for them. No good social interaction or friendships. Mental illnesses that are simply drugged into compliance if treated at all, without any attempt at getting to the root issue. And non-stop 24/7 bombardment by the media with "bad news" that will make someone on the edge only feel more hopeless. I think these sick, sad people just want a way out, and they pick something that will insure that they are remembered, and let them hurt others the as badly as they imagine the world has hurt them.
I don't think you'll ever be able to prevent mass shootings completely. But I think stronger families, and better social interactions for kids would help a lot in preventing them. Being raised by TV and video games isn't good for anyone. And better mental health care for people with issues. Guns are just the tool used when these people break. Its not the problem.