More people are carrying guns though, and yet overall violent crime has been falling.
It's not the gun.
Guns are tools, they aren't the problem. We need to be better at being able to detect these individuals who are likely to go on these rampages. But more than that we need to have a society that is better able to defend itself. If even 1 in 20 or fewer teachers at a school were people who were responsible and trained and carried guns for self-defense then these sorts of attacks would be far less common. Because the attacks would be ended sooner by armed citizens acting in defense. And because then schools and other places would no longer be defenseless. The reason why these crazy people go to schools to commit mayhem is because they know that they aren't going to be stopped. They know that it's just going to be unarmed teachers and defenseless children. If that stopped being the case, if there started to be more of a risk to the shooter in these situations then maybe these sorts of shootings would be less common.
We've spent the last half century in the developed world progressively making ourselves more and more defenseless and less and less empowered, on the premise that doing so also disempowers the bad guys. The rage killers, the school shooters, the terrorists, etc. But the exact opposite has come to pass. We've disempowered the individual and made ourselves defenseless and even more vulnerable to these monsters.
No, not everyone should own a gun, or be allowed to own a gun. But if we started to cultivate more of a culture of self-reliance and personal responsibility, and if we started increasingly empowering individuals to take care of their own self-defense by becoming more aware, more trained, more prepared, and to carry weapons if they so choose then maybe we'll actually end up with a safer society.
I've been shooting guns since I was 10 years old, and I've been carrying a pocket knife since middle school. I take these things vary seriously. I maintain my certifications and training in first-aid and CPR. I have well stocked first aid kits in my home, car, and backpack (when I ride the bus or bike), including things like hemostatic compounds. I also have a concealed carry permit (which means that my info and fingerprints are on file with local law enforcement) and own firearms. If you make a law which limits my capability to defend myself or others then you are not making society more safe. And almost any gun-control law is going to preferentially disempower good people like myself while having much less impact on the bad guys who don't care about living within the law.
Edit: the concentration on guns as an item which "enables violence" is no more sensible than the TSA's concentration on liquids or nail clippers. It's just another form of security theater.