A crime so horrid ...

... that he pleaded guilty and accepted his fate of dying while incarcerated, rather than have his parents hear about what their son had wrought.

It's not an excerpt from a play, book or movie. The man who killed Alan Shalleck, one of the co-writers of curious George, had done so in such a gruesome manner that he rather accepted a lifetime in prison, than put his parents through trial.
And if you know where you're reading this, you probably already know he didn't abuse a gun.
(Man gets life in "curious George" killing, CNN)

"One of the reasons Ditto took the plea was so his parents would not have to sit through a trial and hear details of the crime, Ditto's attorney, Robert Gershman, told The Palm Beach Post.

"It was a horrible, horrible crime scene," Gershman said.
Shalleck had 83 blunt force injuries and more than three dozen stab wounds, including to the abdomen, neck and groin, an autopsy revealed."

Some people aren't quite as civilized as we make them out to be, as we'd want them to be. Allowing or disallowing them to have firearms would not keep them from hurting you or anybody else, once they've set their mind to it.
Disallowing YOU from having a firearm and using it to defend yourself, *would* leave you at their mercy