Talk politics.

If I can, let me use a bit of a tortured analogy:

If a car thief wants to steal my car (like, he isn't looking for just any car, but my specific car, for some reason) he will get it. It doesn't matter what kind of security measures I put in place. Given enough time and effort, he will manage to get it.

Does that mean I don't use security measures at all? Of course not. A steering wheel lock will not deter a dedicated thief - but the average thief is looking to get in quick, get out quick, make a minimum of noise and attract no attention. He sees the lock through the window, he moves on to the next car. I can't stop every thief, but I've stopped most of them.

The gun debate is similar. I've mentioned in replies above that guns aren't the only problem, of course. But at the same time, guns are part of the problem. I'm not in favor of absolute bans. I don't believe that an Australian or British solution would work here. However, that doesn't mean that all restrictions are useless. I often hear the argument that "criminals won't obey the law" and so any and all restrictions will fail. Yet we restricted fully-automatic weapons quite a long time ago. Nowadays, it is very hard to get one - almost all of these mass killings are carried out with legally obtained weapons. I'm certain some criminals out there own some, but we don't see them used on a large scale. The opportunity cost is far too high. Someone planning one of these attacks will not want to go through the difficulties of obtaining one - they will go for easier options.

I also hear that "they'll find some way to carry it out regardless." Perhaps. But again, the harder we can make it, the less deadly the options we give, the more chance that the death toll will at least be lower (or slower, so that help can arrive) or that a potential killer might actually look at what's required and say: "that's too much work, I'm going back to ranting on the internet."

As for specifics, I think things like magazine limits, removing the "ban" on the CDC researching the problem, hell, I'd even be willing to discuss licensing requirements for all weapons (unlike Florida, my own state, where owning a shotgun or other "long gun" requires no special permit or license.) I own a shotgun, and I'd be willing to go through a licensing process to continue to own it.

Obama's proposals were good too. I like that he's taking executive action. The problem is, that's not sustainable. The next President can just reverse it, and some of what he proposed is unfortunately kind of useless. What I want to see is real legislative action. God, if they'd even just fund the damn CDC and allow a comprehensive study of the issue, but even that's hugely politicized.

Regardless, there are more things we could do. We wouldn't stop all mass-killings, not without addressing larger cultural problems then just "guns," but we could reduce them, and I think do so to a notable extent. And every life saved thereby would be worth it, IMO.