A gun was designed to fire a projectile.
So is a nail gun, or as we learned in No Country for Old Men, a captive bolt stunner. Which was designed to kill cattle, but works fine for people apparently.
There are people, including Olympic athletes who have never used a gun for anything but punching holes in paper. Those guns usually include the word target in the model name and have grips and triggers that are designed for the sole purpose of precision shooting and would be almost useless for trying to injure a person with.
Dick Cheneys hunting buddy would tell you that a shotgun meant for waterfowl isn't something that will kill you even though you don't want to step in front of one.
My pistols aren't designed for killing people, that's just what I have them for.
It's about intent. Sure, bad guys pick firearms because they're easy to use.
So do the disabled, the elderly, a large number of women and anyone of slight build. A gun is a hell of an equalizer if you're willing to pull the trigger.
A garden weasel was designed to quickly tear up weeds and aerate soil but if you don't think I could kill someone ask any of my neighbors why we don't have a possum problem anymore.