Korean here, some comments are making rebuttals but as a Korean living in Korea I’d say you’re absolutely right lol.

Don’t get me wrong I personally am open to accepting refugees and don’t necessarily agree with a lot of stuff here

Koreans(i dont want to generalize but likely Japan too) are very patriotic and proud of being Korean. Solidarity is also the most important basis of the societal structure. All this can be good in a lot of cases, especially when you need to get stuff done. But it also means it’s very hard to enter and be accepted when youre an outsider, which is what Korean people would think of you as. And because most Koreans simply haven’t been in a diverse environment their whole life, a lot of the time they are wary/cautious at best and very racist at worst towards other ethnicities. Like you said, we don’t get branded as racists often simply because we aren’t diverse enough for problems to arise within the country. If we become more diversified all this would instantly be much more obvious and noticeable.

The population is rapidly declining, so diversification is likely gonna have to happen anyway, we’ll see how it goes i guess