No one needs these weapons except police and military, they serve only one purpose, to kill many people quickly.
See the quoted comment below. Or did you mean that the police and military only serve the purpose of killing many people quickly?
But rogue local police? Yes, that can happen.
Why an exception for police to have military grade weapons? Who are they going up against? The now magically law-abiding criminals who have turned over all their banned weapons? Or the now unarmed general population? Police also have NO NEED of military weapons, IF you succeed in disarming the law-abiding.