what a word we live in in which something that is known to fire multiple bullets indiscriminately and is capable of taking lives is not useful for self-defense
you could fire an 'automatic' weapon in self defense. but why though? why would you do that? in what way does a shoulder breaking recoil machine make it easier to preserve your life? First shots are almost always enough to incapacitate, and with a bump stock weapon you'll probably land the first shot and nothing else after that. So why not just pick up an actual self defense weapon, like a sidearm?
That excuse could fly if you were fighting off a horde of 50 robbers who all decide to break into your house at the same time, but who would have the time to draw a huge rifle from under their pillow?
Bump fire stocks are purely recreational, impractical, probably for gun enthusiasts like someone who goes to the range or likes mowing down 100 people from a hotel