Humans, it seems, are extremely uncomfortable to admit that a member of their own can commit such vile and egregious acts against another of the same species. We try to attach blame to something, anything, as long as it's doesn't question the very sanctity of our species, and more importantly, our own self centered ego of what it means to be human.
You see it all the time, whether the blame is put on an ideology, religion, guns (as we are seeing in Vegas), lover betrayal, debts, or even a mental illness. Yes, all of these are "cop outs", a way for the average person to distance him or herself ideologically from the perpetrator, since physically, we are inescapably identical.
Why can't we come to terms with the truth and reality of human tendencies? The fact that we are all capable of such acts if we were put in certain circumstances (unknown to ourselves or others). And that any weapon used is not a separate entity with its own intentions, but merely an extension of our psyche. Most importantly, why can't we concede that there is absolutely nothing we can do to prevent attacks on humans by humans?
Take away the shock, awe, anger, blame, and grievances, and understand "it's just another day at the office [of human evolution]".
We are highly flawed. Wishing [otherwise] won't make it untrue.
additional thoughts Would like to add. A lot of respect for the police and first responders. Running into fully automatic gunfire isn't trivial. I wouldn't do that for a Bill Ackman salary. They deserve to be paid much more.