The words of a fool. Muskets and flintlock rifles were the "assault rifles" of their day. Any wound usually resulted in a screaming death from sepsis, or an amputation that didn't kill you from gangrene if you were lucky. Today, a far higher % of gunshot victims survive and return to full activity than they ever did in 1780.
As far as the "rapid fire" feature of semi-autos, even in 1780 any lunatic could take a 1" bore goose gun, load it with rusty nails, and unleash it on a picnic or church. If anything, the results would be more horrific than an attack today with modern weapons, given modern medical advances.
Anyway, the entire point of the 2A, in the words of the founders, was to permit the citizens to be as strong as any standing army, in order to prevent the rise of unchecked tyranny.
I shudder to think that you don't grasp this.