I'm a firearms enthusiast and collector as well. Guns don't make people bad. Bad people use guns to do bad things. Good people use guns to do good things. Like hammers and axes and even fists, there is nothing in this world that a bad person can't turn to an evil end, but that doesn't make the tool they use evil in and of itself.
It's hard to imagine one person, armed only with an axe, hammer or fists being able to kill a dozen people, and wound dozens more, in a movie theater with numerous military veterans and young athletes in attendance.
Funny thing is, there are tens of millions of guns in the hands of tens of millions of Americans, yet situations like what you are describing are exceedingly rare. They are so rare precisely because normal people don't do such things. The evil individuals who do seek to commit such crimes are not limited to using a gun, far from it.
I could drive my car into a cafe and single handedly murder a dozen people, and wound many dozens more. In fact I could do this with my car far more easily and effectively than I ever could with a gun of any kind. Guns take skill to aim and shoot. People tend to duck and take cover, and a few might even shoot back at me. An automobile hurtling into a crowd depends upon nothing more than mass times acceleration. Events of precisely this sort do happen from time to time, yet no one calls for cars and trucks to be banned. No one attempts to blame GM.
If you don't like guns, you're free not to own one. You're not free to deprive other people of that fundamental human right.