You will never predict human behavior perfectly, and I don’t think anyone is claiming that they can. But there are some clear risk factors that we can be better about getting reports from states into the national background check database. Right now, many states don’t report any data, others are months out of date.
People with known psychiatric issues that make them a danger should clearly not be sold a gun. People fresh out of jail on parole for a violent offense should clearly not be sold a gun. I don’t think many people would disagree with some of those basic criteria. And yet, we know the federal database isn’t being updated by every state in real time. And some states produce inaccurate data, which in a way, is even worse than out of date data.
I’m not in favor of reacting to every spree shooting with massive gun control, but I think everyone should favor us doing a better job executing the one’s most people agree with like background checks. Most gun owners (according to polls) support background checks. Let’s all agree that we should do that better.