The purpose of all guns was to kill human beings. A gun is a weapon.
I can kill you just as easily with a six shot revolver as I can with an M60 machine gun.
I mean, seriously, how do you make that differentiation? A gun is a damn gun. They got more sophisticated, with more fireable rounds, as the times necessitated bigger and better guns.
You only see a difference in how many people can be killed. I could load up with kevlar, take a couple pistols out to Times Square, and kill just as many people as a dude with just an AK. Where you would be justifying my ownership of said pistols, and arguing against the AK, the same amount of people were killed. Why is that?