If we were going to ban guns as a public safety measure, we really should start with handguns - they don't look nearly as scary, but are responsible for the vast majority of gun-related deaths. And that holds true even if you only look at gun deaths caused by mass-shooters who own an "assault rifle". Handguns are after all a weapon specifically designed for killing civilians in urban environments in the most convenient manner possible.
Assault rifles and their kin on the other hand are optimized for killing armed and potentially lightly armored adversaries at medium range (out to a few hundred yards), and are drastic overkill for soft targets at closer range. Eliminating them primarily helps protect police and possibly gang members, not the general public.