There's still not much good information about the horrific massacre in Connecticut, and the facts in these things can change at an alarming pace. So I'm not going to pretend that this post is anything more than a jumble of thoughts. Really, I'm mostly writing this because it's less bad than the other option, which is repeatedly refreshing news sites to get the newest painful details.
1. You can kill a lot of people with any kind of gun in the right context. Right now, it seems like this is the variety of gun the shooter used: a Bushmaster AR-15.
It's big and scary-looking and the idea of one of these even being within a hundred feet of a kid makes me queasy--but it's not an automatic. It didn't have to be. Semi-auto AR-15s kill people pretty efficiently, because that's what they were designed to do. When they were developed, they were lauded for their ability to cause grievous exit wounds. Don't think about that.
And there are, in fact, lots and lots of guns that are designed to kill people efficiently. Pretty much anything that isn't a long hunting rifle can facilitate an atrocity in a sufficiently crowded setting.
Just something to keep in mind when crafting a policy response.
2. Marginal improvements help. Building off the above, it should be clear that there's no perfect way to stop these things from happening. Even a total firearms ban--political and legal infeasibility aside--would leave many millions of guns in circulation. But that's a reason to look for solutions at the margin, not to throw up our hands.
Fewer large magazines mean shooters won't be able to tote private arsenals around with them quite so easily. Fewer concealable guns limit wielders' ability to move in and out of public locations. Restrictions on sale don't prevent guns from circulating, but they'd surely raise the price of firearms--on the black market or otherwise. Stepping up enforcement does the same. And so on.
Is there an appropriate mix of rules that will stop every incident? Almost definitely not. But if your goal is simply preventing as much violence as possible, each little rule, restriction or limit on gun ownership helps.
3. The "armed bystanders could have stopped it" argument should be gone for good. Unless you want to arm schoolteachers.
More than that, the mere existence of children should remind us that not every potential target can be hardened.
4. Mental health plays a role, too. Like the points above suggest, I'm basically in favor of getting rid of as many guns as we can. But the shooter didn't just wake up today possessed by an evil spirit. Something happened in his mind to make him do this, and limiting the capacity of people like him to hurt others doesn't prevent us from trying to keep people like him from wanting to, as well. I don't know if the guy was just an angry kid whose view of the world was warped beyond recognition, or if he had actually taken leave of his senses thanks to some underlying mental health issue, but there's no cognizable motivation that we don't have an institutional response to.