People tolerate differences from themselves poorly. So homogeneous cultures are likely to have less violent crime than heterogeneous cultures. The fact is that there are many issues of violence and crime are cultural. Many like to compare Japans gun crime to America as a way to vindicate their views on the gun control issue. I think it only demonstrates their tragic ignorance.
Japan is one of the most homogenous and intolerant societies in the world.
We should not mimic them, and thankfully would not tolerate their brutal justice system, or cultural attitudes in general. If it was just guns that were the cause of crime, then there is no explanation for the Switzerland Paradox. Of course they have a more homogenous society, and are not nearly as tolerant to outsiders as the U.S. is. They also don't have the tolerance for crime or criminals that the U.S. does either. And of course there are many other factors like they have more people trained in proper gun usage, they tend to live in more communities than the U.S., and so on.