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.
But a pistol is just as usable for illegal activity, if not more. They are small and compact, making them much less noticeable.it's harder to commit mass murder with one.
Are we really only concerned about mass murders? I get where you're coming from, but it's really easy to justify really harsh restrictions based on the same logic.
http://en.wikipedia.org/wiki/Virginia_Tech_massacre#Attacks 33 dead and 23 injured.Pistols can of course still be used to commit crime but it's harder to commit mass murder with one.
Cho used two firearms during the attacks: a .22-caliber Walther P22 semi-automatic handgun and a 9 mm semi-automatic Glock 19 handgun.