The "homogenous" trope is just that. I live in a city (Vienna, Austria) of 1.9 million people where 50% are 1st or 2nd generation immigrants. A huge proportion of those immigrants are brown.

Yet we have extremely low violent crime, and virtually no gun crime. Why? Because regular people can't buy guns. If you get a permit for a gun, you sure as shit can't carry it on the street.