Also, the people saying "Don't let immigrants in, Japan!" are largely immigrants like me, already in Japan--often calling themselves expats (bc they think it sounds better than "immigrant"), and what they're really against is immigrants who aren't white.
The other common commenter on news stories about immigration are people who have only visited or maybe only dreamed of visiting Japan, and have this unrealistic vision of Japan as utopia. They weirdly want to "protect" Japan, and often say things like there should still be samurai...
And of course there are the Japanese commenters, but not so many under English-language news articles. The first two groups annoy me much more: the pick-me expats who want to pull the ladder up, and the racist Japanophiles who know very little about the reality of Japan.