As you properly note, holding a rifle in cyclical fire takes strength and dexterity the disabled lack. But the disabled CAN use their body, with the aid of the stock, to fire the rifle accurately for a single shot.  Those without a disability don't need the bump stock to fire the rifle faster. I'd be willing to bet even you have the smarts to make a hand crank with a couple of lobes that lets you substantially increase the rate of fire for a semi-automatic rifle or handgun. Think someone who has chosen to commit mass murder at a concert is going to say, "Oh darn, cranks are illegal now, and making one would be against the law. Guess I'll have to abandon my plan now."? Yeah, me neither. So exactly how would this proposed law stop the next lunatic again? The only effect of the law would be to deny to the law abiding the enjoyment of experiencing continuous fire without the 5 figure price tag attached or having to pay an outrageous amount of money to a business for it.