Wow. This is a truly horrifying attempt to normalize racism. "If you don't like it, just go home." He's been there for a decade. The author likely sees Japan as his home.

The social mechanics of Japan are certainly quirky by western standards, but that doesn't mean that some things aren't universally unacceptable. You might as well say, "If you don't like persecution of gays, stay out of Nigeria." "If you think women should be able to drive, stay out of Saudi Arabia." (recently changed)

As a traveler, and someone that's been to almost 50 countries, I tend to keep my head down and not make waves when I'm out of my the cultures where I feel at home. But that doesn't mean that I can't write about injustices. That's what you're literally saying the author is not entitled to do. After a decade in said country.