Every rich country has drugs, every rich country has crime, every rich country has minorities and immigrants - though admittedly, Japan and South Korea are fairly racially homogeneous and have been more hostile to immigration historically.
It's not a great argument because Canada (more immigration, more diversity than U.S.) is still doing a lot better than the U.S. on gun deaths.
So what I conclude is that when you stir all of the above together and add guns and you get more gun deaths. Stir all of the above together and don't add guns, and you don't.