One thing that we have is a drug problem--and I don't mean street drugs. I have read a number of reports about these mass killers, and many of them are on prescribed drugs. The children in school massacres are taking Ritalin or Prozac, or some derivative of the above. Why? Because they could not sit still in class, and refrain from integrating the disjointed percepts that they are being taught into concepts and puzzle pieces. They are then called in to be prescribed drugs for this condition, and the drugs make them prone to violence.
Then there are the "kick crimes". These are the ones involving someone doing things for kicks--vandalism, harassment, reckless behavior, and often stealing are among these. They are bored, stagnated, and need alcohol and/or drugs to release themselves from this stagnation. This leads to petty crimes, and those often escalate into murder. If you take away the stagnation by removing every single one of the "hot laws", you sharply reduce "kick crimes", drug use (and that without a single drug bust), and the petty crimes as well as the impetus for them to escalate.
What that leaves are the criminals that insist on initiating the use of force to get control of people. If ordinary people would have the means to defend themselves against these humanoids, then people would think twice before trying to rob someone. Those that are insistant on controling others by force would be shot, and the common citizen would be that much safer. There would still be laws against initiating use of force against people, and one would have the right to kill someone in defense against such. People would think before launching that first-strike offensive attack. And, eventually the guns would simply sit there unused. At which point, most people would be willing to drop that extra weight and bulk that they take up. Problem solved.