I think it was Michael Medved who touched on this reasoning, too. He said that conservatives look at the morality of the user; guns are not good or bad, it is the person holding it that is good or bad. Nukes aren’t bad in and of themselves, but nukes in the hands of Iranians are bad while in the hands of Americans are good.
Liberals are materialist. They don’t think of good and evil in spiritual matters, mostly writing off the soul. If there is good and bad, it is based on the feelings of each person, and thus impossible to be universal. But THINGS, materials objects, that can be used to hurt others are bad. To a liberal, you cannot decide if the other person is good or bad since that can change. But liberals can decide that all guns, all knives, all bombs are bad. And they assume that if you get rid of all the bad THINGS, then people cannot do bad no matter their impulses.
The evil gun trope was made into a movie in 1989 with "Blue Steel" starring Jaimie Lee Curtis and Ron Silver. Silver played a guy who took a gun from a robbery scene. Taking the gun turned Silver's character into a homicidal maniac. I think many libs seriously believe mere possession of a firearm turns normally nonviolent people into pyschopathic killers.