I don't think "bump stock" make a "machine gun",but they damn sure make a dangerous weapon.
I know I am going to be stepping on some toes here,but the damn things are both dangerous AND stupid.
It's almost like some goober created a "goober think tank" to solve the age-old questions,"What can we do to make a firearm BOTH more dangerous and less accurate?"
Not to mention useless.
BUT.........,"Yes,I DO agree that it is the business of our legislature to have the final word on this sort of thing,not some fumbling and bumbling un-elected bureaucrat.
Regardless of whether it is a good idea, the question is one of whether the stock makes a semi-automatic rifle a machine gun.
NOPE.
It doesn't. It makes no change in the number of times the trigger must be actuated in order to fire the rifle. Once for every round fired.
It makes actuating the trigger more efficient to achieve the maximum rate of fire out of a semi-automatic rifle. That's all.
That is the question to be decided, not whether these devices are a particularly good idea.
I can see where, with practice, someone could learn to limit their fire to short 'bursts' (as opposed to dumping the magazine ), and learn to correct aim on the basis of impact instead using the sights, but that sounds like employing a machine gun.
How dangerous a weapon is depends on who is holding it.