Why does the US have so many more “bad guys” than other developed countries? What does that say about us?

I ask because we have the highest rate of gun deaths in the developed world and because Republicans and Trump supporters insist that we can’t have any more gun control because “guns don’t kill people, people kill people” and “we don’t have a gun problem, we have a morality problem”. Why do we have a “morality problem”? I thought we were “the greatest country on Earth”? So we’re the greatest country on Earth, we just have the shittiest people?