EXACTLY! I was mentioning to a friend a while back that I don't know why all these man-made tragedies like mass shootings have taken so long to start. If you start from "There isn't such a thing as a god" the logical endpoint is "nothing I do matters, so why should I work so hard to survive instead of going out with a bang?" And with everybody around you ALSO being a freak accident of nature, there is no reason to respect their right to live either. In fact, who came up with this whole rights thing in the first place? Why should any cosmic accident have rights?
If you take God out of the equation, the only thing left holding society together is force, usually manifested in armed police officers, and they can't be everywhere all the time. And I think their job is about to get a lot harder, because a lot of people are starting to wake up and say, "Hey, why shouldn't I do that too? Except school shootings have been done so much nobody pays attention anymore... I should do something bigger, something different, that will get people's attention."
Why not? If we're all accidents of nature, none of it matters anyway.