you're comparing a trained marksman, (who actually recognized his own mental illness even as he proceeded to kill) to a series of very deranged "kids" with excessively capable semi-automatic weapons
said by NormanS:
No semi-automatic "assault" weapon there....
... Removing that weapon type won't stop mass shootings, it will only stop mass shootings with that weapon type.
A lot of people in Colorado and Connecticut and Arizona and Wisconsin, etc. would be happy to start with that.
Nobody expects to disarm any existing owner (barring threats, irrational behavior, or criminal activity), and most weapons would still be available with the hope of buybacks and voluntary turn-ins removing/reducing big clips and certain weapon and ammo types overtime (If you don't think your kids are responsible, you shouldn't will your weapons to them, or ebay them to persons unknown)
The idea that we shouldn't start the process with some particularly dangerous weapons, because some would still exist is silly Should we also sell fissionable material? just in case you feel really threatened , by the new neighbor or gang down the street