Its all about the lines isn't it?
We should be able to own guns, but what kind of guns?
Should we be able to own artillery? Grenades? Tanks? SAM's?
Should we be able to own .50 cal machine guns?
Fully automatic weapons?
How is an AR15 equivalent to a grenade or a tank? It shoots a very small bullet one at a time. It is not a machine gun. Maybe the feds should have machine guns, grenades and tanks but citizens should go back to using a bow and arrow.
The issue here should be what makes someone decide to kill a bunch of people. The tool that they choose to use should be irrelevant. Bombs are outlawed but yet a couple of nuts used them in Boston and killed people. If it isn't this weapon it will be that weapon. You shouldn't penalize the overwhelming majority of sane, responsible people because there are some nuts out there.
We are talking about people that are equipped to do other people harm. As a man with a dick, you are equipped to rape women. A lot more rapes happen every year then mass AR15 shootings. Should we start castrating all men? After all, they could snap and start raping women. If men didn't have cocks we could virtually eliminate rape.
The government can not protect you from all potential harm. A better choice would be to learn how to protect yourself.