Bump stocks are essentially a "horizontal pogo stick" which allows users to shoot a semi-automatic weapon like an automatic weapon by bouncing the trigger off a stationary finger to replicate a rapid-fire mechanism. It allows shooters to fire many more rounds per minute.
On October 1st, 2017, Stephen Paddock committed a mass shooting at a country music festival in Las Vegas using a bump stock mechanism. If he had not had access to a bump stock, he would not have been able to kill anywhere near as many people in the time it took for armed units to respond. Bump stocks should be banned to reduce the loss of life in mass shootings.
Banning bump stocks will have almost no effect on the lethality or frequency of mass shootings in America. Firstly, they are not even that functional. They often lead to the weapon jamming or misfiring, and significantly reduce the accuracy of the weapon. In fact, not using a bump stock would probably lead to more deaths in the event of a mass shooting. Secondly, if someone has decided to kill a lot of people in a mass shooting, the lack of availability of bump stocks will not change their mind. There will be just as many mass shootings, involving just as many killers, who will kill exactly the same number of victims, if not more.
The state has the right to mitigate access to things that could be harmful.
[P1] Bump stocks increase the volume of rounds a weapon is capable of firing per minute. [P2] This makes them valuable to those carrying out mass shootings. [P3] They should be banned to mitigate loss of life in mass shootings.
Rejecting the premises
[Rejecting P3] Banning bump stocks would not mitigate the loss of life in mass shooting incidents.
William Tyler Gilbert, Calling a Spade, A Spade: Infirmities Facing Bump Stock Regulation under the National Firearms Act, 107 Ky. L.J. 705 (2019).