Trying to turn this into:
- Harsh punishments stop crime: doesn't work because we've tried it for thousands of years and we even tried it in the 90's and no credible paper says that's the reason for the subsequent decrease.
- Cultural homogeneity is the only solution so west is fucked: is just a non-starter explanation and doesn't lead anywhere to solving the issue. It is also stopping shy of actually explaining anything. If homogeneity were "the answer", then it either it is just a confounder or the foreigners are doing vastly more crime than the citizens.
I'd suggest that actually the underlying issue at hand is that everyone is trying to get simple easy to understand answers. That this idiotic belief that the world is simple is why we're grinding so many gears. Nearly nothing in the modern world is simple. We've solved those problems a long time ago. We had thousands of years to work on these and it should make sense that the simple problems got solved first.
What's going on is now people's propensity to both care too much and too little is harming us to such a degree that it makes problems too difficult to solve. People care enough about these problems to make strong statements and virulently fight one another. But at the same time they don't care enough to look into the problem and try to understand any nuance or depth to it. When they end up doing so they often turn to conspiracy which ends up being another easy explanation such as "wizards did it." The classic "if it weren't for 'them' then everything would be solved." Which is closer to this homogeneity argument, since Japan has a lot of problems (as well as good). It is easy to romanticize places. The clique works both ways: the grass is always greener can be about your neighbor's lawn compared to yours or the other way around. Seemingly paradoxically they can both be believed by the same person. If only the world were that simple, where at least such a claim is measurable.