You don't disagree. There's a crucial element that proves multiculturalism is heavily immoral. Read this line again,

In fact, take everything you've written down and multiply them by three. Because when you introduce diversity, you are forced to now deal with many ethnic groups and their issues as opposed to just helping one.

Multiculturalism literally costs money. It's not cheap and it was never affordable. In America alone, we've seen race riots since the country was founded, all the way to 2020 today.

Japan NEVER had that. Only in multicultural societies, does racial violence exist. Only in multicultural societies, does racism exist. Racism can only exist because diversity enabled it.