The reason you shouldn’t been weapons is very simple - you can’t.
Look at alcohol prohibition in the early 1900s. Virtually all alcohol production, storage, transport, sales, and consumption were banned. And what happened? Did people stop drinking? Did crime go down as predicted? No, quite the opposite. Crime went up because criminals now had a market for illegal goods. Prohibition was where organized crime got its real foothold in the USA.
Same thing is true with weapons. If you ban weapons, all of the law-abiding people will turn theirs in, and the criminals will not. This does not improve public safety. In fact it reduces public safety because now the criminals have weapons and the means to acquire more weapons, whereas the law abiding citizens are unarmed.
Why would you think that? That a psychopath who often spends weeks or months planning to kill people is going to be dissuaded by that, when there are black market ways to purchase or construct a firearm of their own?
Evil men will always find the tools they need to dispense their evil.
Actually school shootings is a good reason for more guns not less. There have been a number of would-be mass shootings that have been stopped by armed Good Samaritans, either off duty police or civilians with carry permits. Much like overall crime, this is a distributed problem and you don’t usually fix distributed problems with centralized solutions.