I've realized we're probably confused about whether we're talking about Japanese in America vs. Japanese-Americans. I was talking about Japanese in America (the article is about a foreigner in Japan), but I'd make roughly the same claims in either case. Empirically, I would bet that both Japanese in America and Japanese-Americans both show rates of criminality more similar to Japan's than to the remainder of the U.S. population's. In the case of Japanese-Americans, I'd bet it's higher than Japan's. I haven't looked any numbers up or attempted to figure it out in detail.
As for why, there are a few reasons. One interesting one is selection effects (immigrants to a new country are not a random sample of the old country's population). There is culture, of course, probably the biggest factor, as well as other inheritances (material goods / wealth, genes, disease burden...).
I'm genuinely curious to know how you think about that line. What is the transgression here in your mind? Merely mentioning that genes affect behavior is not allowed (even though it's true, or maybe it doesn't matter if it's true), or you actually believe the claim "genes affect behavior within the human species" is false?
I agree with you that we can't tell from a single gene whether someone is likely to be a criminal or not. I'd like you to consider this example, where hopefully I only use premises you already believe:
Some people are predisposed to becoming addicted to drugs. We can make better-than-chance bets about who these people are based on their genomes. We also know that people who are addicted to drugs are more likely to be on the wrong side of the law (and, sadly, are often by definition on the wrong side of the law). So, we conclude that, given someone's genome, we can make better-than-chance bets about that person's likelihood of being on the wrong side of the law.
It's a simplistic example, but hopefully that helps get the idea across. Doing this sort of thing isn't super practical right now, but it will be soon! [oh boy.]
Genes are certainly affecting the behavior somehow. That doesn't mean they are relevant. Cultural and educational factors have certainly a much bigger impact on behavior than any gene related effects.
Example of flawed reasoning similar to yours: genes have probably an impact on the way we speak (it's impacting the shape of our tongue somehow, etc etc). So maybe the French have their accent due to some genetic factors, and we could predict someone's accent looking at their genes. Well it turns out in practice, if you have "French genes" and are born and raised in a US environment, you'll have an American accent indistinguishable from someone with "US genes"
If genes are affecting behavior [I assume you mean variation within the species], then why wouldn't they be relevant? Relevant to what?
I agree culture is the biggie (education is part of culture).
Your example gets at a correlation that can be used to make good predictions. Better-than-chance bets. The example I gave with drug addiction supposes the reader already believes that genes have a causal relationship with drug addiction. That is, a propensity to be, say, an alcoholic can be in your genome and not a result of environmental factors.
Given this logic if America had a policy of throwing everyone with blond hair in jail for "hair crimes" you would conclude it is a fairer system than Japan's if Japanese-Americans had a lower incarceration rate than Japanese people in Japan.
That's some heroic effort in defense of America's high incarceration rate.
Further up on this thread someone wrote "If you ever thought the American justice system is bad...".
Someone else wrote wrote " Not trying to handwave away issues with the Japanese system, but scale seems relevant here. Japan: 40 incarcerated per 100k population [1] USA: 655 incarcerated per 100k population [2]"
So I read your post in that context. The conversation seemed to me to be about whether the American or Japanese justice system is "bad". Fairness would seem to be an aspect of "good" or "bad"... if you weren't trying to argue the American justice system was "good" I've lost the context of what you were trying to say.
As for why, there are a few reasons. One interesting one is selection effects (immigrants to a new country are not a random sample of the old country's population). There is culture, of course, probably the biggest factor, as well as other inheritances (material goods / wealth, genes, disease burden...).