The Japanese simply protect their culture, because they know that once you have Islam in your country they always try to change that country to Islamic values, and these people do not hesitate to use violence in the process. It's already sort of going on in Europe and the United States. Japan is smart in this regard. Only a few Muslims each year are allowed to get a (permanent) visa and/or become official Japanese citizens. Europe is less smart, the birth ratio among native Europeans is much lower than in Muslim families, so in the long run the original people will be replaced. Christianity disappears, Jews will flew again, and Europe will contain nearly 1/4 Muslims by the year 2050.