I'm not sure why it is so necessary that we identify a culprit in all of this. What good does it do us to know that he is, say, a paranoid schizophrenic? It may matter in his sentencing, of course. But it's far from clear that this knowledge would let us do what we want, which is to prevent this sort of thing from happening again. We are not going to prophylactically lock people up, and there is no "seems a little, well, off" list to which we can add people we don't want to have guns. Even extended magazine bans wouldn't have done much good, as he was carrying lots of spares. As I understand it, he was essentially stopped because one of his spare magazines malfunctioned, something which may be more likely to happen on larger capacity magazines. Anyone who practices a little can swap magazines faster than others can notice and decide to tackle them.
Blame is a way of simulating control: if we can just identify who was at fault, we can stop it. The problem is, when we can't identify any very plausible target, we too readily go after implausible ones: Freemasons poisoning the wells, or Federal Reserve bankers plotting to monetize the national debt. At worst, this tendency is dangerous, corrosive; at best, it leads us to make unproductive policy choices.
A terrible thing happened. We live in a universe in which terrible things happen. That's no one's fault--or maybe, everyone's fault. Either way, I don't see much in the way of solutions coming out of this--only terrible, terrible sadness.
This kind of fatalism makes for good fiction, I think, but not terribly good policy.
Not being sure why it’s necessary to identify a culprit seems like a reasonable stance in instances in which a culprit is difficult to identify. But of course once you do identify a culprit you can begin to assess your options; it’s clear that the writer understands this as she moves through quite a few hypotheticals and counters with quite a few objections, some of which I suppose are well-taken. But the very act of proposing hypotheticals makes it clear exactly why it’s necessary to assess what’s at fault—in this case the writer seems to believe that the policy solutions would not be worth the sacrifices necessary to enact them; but you still need to try. The attitude that bad things happen and always will has a religious cast and is worth keeping in mind, but ignores degrees—and therefore isn’t terribly productive. Otherwise we’d still be living with all sorts of evils in our midst.