Don't these countries have lower murder rates than the US has non-gun-related murder rates? As in, even if you removed every gun in the US, and even if all the crimes that would otherwise be committed with guns now just don't happen, the US still would have a higher murder rate than these countries.

(This is off the top of my head, please correct me if I'm wrong.)

In which case, it seems unlikely that the US' murder rate can be attributed to guns. You don't explicitly blame guns yourself, but I think this is worth noting. (And "civilization and the rule of law" isn't a solution, it's an applause light.)