Edit: I know HN guidelines say not to complain about moderation (I've been here for 13 years now), but it's ridiculous a very simple, on-topic question should be downmodded into oblivion on a site whose purpose is discussion. While I have karma to burn and will happily keep participating, I'm concerned that this trend will have a chilling effect on people who do not.
You observe similar criminality trends in African immigrants to Japan compared to the other immigrant groups (including Europeans and Americans), for example. The only exception is the Brazilians, who were brought in as low class workers, have a MUCH higher crime rate, have trouble renting outside of low-income areas, can't get high class jobs, and are generally treated like criminals on-sight.
Germany has a similar problem with their Turkish population.
And it's not restricted to skin color, either. Low class culture takes generations to clean out. I've had a number of dealings with shady descendants of American-Italian immigrants, many in high level financial market jobs. This is fallout from the exclusion of Italian immigrants from the higher classes in the early 20th century, which led to an undercurrent of criminality in their culture (not to mention their good positioning during alcohol prohibition, gambling prohibition, and later drug prohibition).
Cultural currents take multiple generations to steer, which leaves one with many chickens coming home to roost after treating a class of people like shit for so long.
I am Italian and I can assure you that those who remained in Italy are not different. Large part of the Italian immigration to the US comes from the south, where the different types of mafia are only the official and extreme degree of a widespread culture of corruption, shady dealings and reciprocal abuse.
Lower class people are excluded from many (and sometime most) parts of society through harassment, violence, ostracism, or even through legal means (India's untouchables are a good example, or Japan's burakumin). As a result, they stop identifying with anyone outside of their class, and not only don't care what violence and misfortune befalls the other class, but are much more willing to contribute to it, given a good enough opportunity.
When you blend poverty and classism, you have the perfect mix for despair, because 99% of people born to this state have literally no hope of ever escaping it, which makes the criminal route a MUCH more attractive option, since virtually every legal means is barred to you by your class, and the few that remain are such long shots that you'll probably waste your whole life chasing them if you did (unless you get lucky).
I lived in the USA for many years and saw it quite clearly: the rage, the despair, the hatred. And I really can't say I blame the downtrodden for their reaction to this kind of systemic injustice, especially since they are treated this way the moment someone sees the color of their skin (the Irish and Italians of old could at least LOOK like the upper class with enough effort). How can someone who is identified as low class on-sight be anything but angry and frustrated?