I don't think anyone is under the impression that the country of Japan is obligated to do what some random Internet commenter thinks.
People are allowed to have opinions that something would be a good course of action or not. That's not paternalism.
The comment was phrased as trenchant criticism of the Japanese on a matter that is strictly their own business, calling them racist & xenophobic and contrasting them to the USA who 'do immigration well'.
Do this, be more like (supposedly virtuous) X and don't be Y & Z is clear paternalism and, in my opinion, highly arrogant paternalism to boot.
I suspect that you wouldn’t react as strongly to a smug assertion that the USA is a basket case.
It’s okay to admit that the US has done immigration well. It has. There are a great many things that Japan does better than the US. We can discuss them without taking umbrage.
Boo boo? I'm not sure exactly why you expect Japan to be held to a different or lower standard than the rest of the world but I don't stop to think about the feelings of disgruntled nationals when bringing up racism in any other country.
What's far more arrogant is you thinking your culture is so magically different that you're somehow immune to such criticisms. I wonder how the Koreans and Chinese would feel about that.
Absolutely, thank you. I don't honestly care what Japan does. I'm not Japanese. I just think that the only realistic solution for them is to increase immigration.
The American government dropped a science fiction bomb on two Japanese cities, invaded, and then dictated the rules of the Japanese state. They continue to have military bases on Japanese soil. Arrogant paternalism?
People talk about it all the time, especially on toxic forums filled with foreigners opining about Japan like r/japan. There are many reasons why immigration is not the silver bullet you think it is (some of which have been given by other replies). But the important thing is that Japan and the Japanese get to decide where to take their society and no one else. Telling the Japanese what they should do is arrogant paternalism.