My argument is that a bump stock circumvents just as many regulations as a quick trigger finger does.
You can still own a full auto as an individual. Takes a pretty penny and about two years of waiting, but you can.
Bump fire, believe it or not, is possible without a bump stock. By your definition, we should ban bump fire altogether. And really fast trigger fingers. And aftermarket triggers. The list goes on.
Of course, gun grabbers don't mind that at all. But that's neither here nor there I guess.