Many people argue that the United States could never get to as low a level of guns as Japan. I find this easy to believe, and it is an argument against radical gun control proposals for the United States.
But say you use this argument, and suddenly you are asked to advise Japan. Should you endorse their gun control regime? Probably. It is hard to believe that Japan should seek to move to the higher-gun equilibrium found in the United States.
Gun control critics often use the "cultural argument," and indeed I do too. But we often the invocation of this argument with a kind of mental and emotional partition. How willing are we to raise our hands and say "I favor gun control in many of the world's countries." Why do we think that these other countries somehow do not count? Why do those cases not disturb our self-images as "gun control critics"?
Note that the more you cite "American Exceptionalism" the less likely your American views will hold around the world and that means your views are really just a special case for a few outlier countries.
It is especially worrying when cosmopolitanites are inconsistent in this manner.