Just because he was holed up and took hostages over the course of 3 hours doesn't mean it took 3 hours to kill all those people. Most of those people were shot within seconds. It was fish in a frickin barrel with a weapon like that, whether you want to call it an assault rifle or not is besides the point. If he "only" had a handgun there'd have been way less carnage. If you think otherwise you are kidding yourself.
AR-15's sure are fun though but so are grenade launchers and large bombs. I suppose we should be able to arm ourselves with those as well.
No. Most were not shot in the first few seconds. The only way you can kill than many people in a few seconds is with a fully automatic weapon. Those have been illegal for citizens to own for decades. If such a thing was capable with an AR-15 you'd have to pull the trigger every second. With recoil, you'd never be able to control the weapon firing that rapidly. So, some who say that an AR-15 can shoot 400 rounds per minute fail to realize that you could never move your finger that fast let alone load new clips since a 400 round clip simply doesn't exist for this weapon. The clip would be like five feet long.
Also, someone skilled with a revolver can do more damage than someone with a semiautomatic with no training. If I think otherwise, it's because I shoot all the time and I'm familiar with weapon capabilities.
Finally, I'd have no problem with citizens using grenade launchers, etc. if there was a justified reason to revolt against one's government. The protections we grant ourselves to own and use guns are primarily entrenched in the American Constitution to allow us to protect ourselves and our property, especially from a tyrannical government. If you can't grasp that basic right then you fail to understand even why we have a constitution.