I think a good judge is how usable is it for legal activity vs. illegal activity. There are very few legal activities that are made easier with an assault rifle. Obviously shooting 850 rounds per minute would make it easier to kill someone attacking you, but compare that to how much more dangerous you are to the rest of the public. Pistols can of course still be used to commit crime but it's harder to commit mass murder with one. and then there is stuff like Civilian legal artillery pieces which are only ever allowed for collection reasons, although a Flack 88 is crazy powerful it's not going to be very useful for doing anything because people would see it coming a mile away.