The problem is the weird cultural phenomena of taking others with you when you off yourself and end your life in infamy. At one time called going postal. As long as the media hypes these sickos there will be follow ups. Notice these sickos usually pick places where legal weapons are banned, airports, schools, etc. When guns are outlawed only the outlaws have guns.
Sorry but i call that complete bullshit.
You want to know what place in the world has the most amount of people "going postal" is?
China. But you never hear about it because 1. it isn´t covered much in the media, and 2. because they rarely have access to firearms,
victims usually survives.
The same was true the last time something like it happened here as well(about a decade ago now IIRC), the perpetrator only had a knife, so there were people injured, but noone died.
And gunlaws here are much closer to USA than China, except for the fact that laws on storage here is much harder. Which means that raiding a house for a gun is nonstarter unless you have the ability to break open a pretty sturdy gunlocker, and sometimes a second separate locker for ammo.
When guns are outlawed only the outlaws have guns. Or as one Bar Fly on Baen's Bar puts it Average response time of police is 15 minutes, .357 bullet travels at 1,500 ft per second (can't remember the number so I chose Mach 2).
And do tell, exactly how often does a private person actually managed to interrupt a "perp with a gun"?
Based on what i know, it is exceptionally rare.
And IIRC, in over 1/4 of the times that it DOES happen, innocent people gets shot, by accident by either side involved or because the private with a gun, misidentifies who is the "bad guy".
Unless you desire a society where flak jackets is the prevailing fashion, this is not a solution, or even a good idea for how to think about it.
And yes you were close with your guesstimate for a .357 V0, they range from 1200-1600 ft/s.
Your maths fail you however as that is nowhere near mach 2. ^_^