What you must understand is that these "bump stocks" don't allow you to do anything with the rifle they're attached to do that you can't do without it. 

An ordinary fixed stock can be attached to the rifle and you can still bump fire it at a high rate of fire. 

The bump stock does make it EASIER, it lowers the skill level required,  but learning to bump fire any semi-automatic rifle (ANY OF THEM) is just a skill you can start to learn in minutes. 

The bump stock does not make it POSSIBLE, it just makes it EASIER. 

Ban the bump stock completely, and it won't matter.  You can still bump fire the rifle with a regular fixed stock, or a collapsible stock, or a folding stock.  IT DOESN'T MATTER.