Clearly you're unaware that this actually backs up the point that I was making and further discredits yours, because it shows that the dying out of specific cultures is not primarily caused by immigration, but rather by changes in social consciousness or in socioeconomic conditions.
In the 2011 census, the White British population of London was 45%, and the White British population of Birmingham was 53%. The fact that you still think London has a richer culture shows again that your perception of culture is much more formed by historical landmarks than ethnic population.
Ignoring your slightly puzzling flourish about me not being able to respect humanity, here is the way I see it. (I am specifically responding to the "preservation of culture" argument from Chou Toshio and Pyritie.)
1) Compassion is morally good. Caring for our fellow creatures is a worthwhile end. People of all nationalities equally deserve compassion, all other things being equal. I doubt that you are arguing from a moral nihilist/relativist standpoint, because otherwise you wouldn't be valuing a "respect for humanity" so highly.
2) There are, and have been, many refugees and immigrants now and in the past who are fleeing from war, ethnic cleansing, abject poverty, or hunger. A large amount of these immigrants are people who do not pose a threat to society through crime or violence and have no ulterior motives, only their own safety and happiness in mind.
If we close our borders to these innocent people, inevitably we will be causing more people to fall victim to whatever they are fleeing than if we open our borders to them. (Again, not concerned ATM with pragmatic concerns about how we can discern the "right" people, just where the moral goal lies). This is immoral.
3) Reducing suffering and increasing happiness are generally compassionate acts; the reduction of suffering is a more important goal than the increasing of happiness.
4) Cultures are able to have immoral aspects. I can prove this by example - treating black people as inferior was intertwined with culture in the USA and still is, and it would be better if this wasn't the case, so it is morally good to strive to eliminate it, even though some people may be attached to, and form their identity around, this part of their culture.
5) Racism in the USA has a rich history, and no aspect of this history justifies its immorality, and I believe the same applies to the ethnic purity that you want for Japan. As I have argued, in a situation where a culture does not match up with what we now recognise to be moral, culture loses and it has to accommodate. Closing Japan's borders to anyone fleeing real danger, and letting them subsequently fall victim to it, in the name of preserving ethnic purity, would be, I believe, grossly immoral.
I don't disagree with your general arguments, and as an American I can appreciate them as objective/rational truths.
However, in the real world, "good" is not completely objective, and justice without consideration/sensitivity for context and specifics is often misguided; affirmative action for instance seems grossly unfair from a purely rational justice, but the context of centuries of slavery and discrimination changes how you need to think about it, right?
You may not realize it, but basing your thinking off of what you see as simple, moral truths is taking those truths for granted, making a gross assumption, and forcing your ethical view on [in this case Japan].
You have to remember that a purely rational view of morals and justice is something born from male, western, patriarchal philosophy-- and while the values you hold now are different from Socrates', you are comfortable with those values and view points because they have evolved from a history that is a history of your own people. What you can experience as "progress" or "progressive", is also an evolution that your own people and community have lived and changed through. Taking that progress as universal moral truth is a form of
privilege.
To get a moral view that has a lesser chance of stamping on "other" groups (such as minorities and foreign countries that come from a completely different cultural heritage) you need sensitivity to context. Simplistically forcing your moral view of the world into another independant country and people is not only imperial, it can have terrible consequences; especially in the unforeseen category.
Maybe, if westerners were better at not forcing their objective view of morality on other peoples, the Middle East would not be the mess it is today-- in my view, an insensitivity to culture and forcing change on a traditionalist culture with a strong preference for little change is a great evil and root of the problem/history that has driven the problems there.
On your point about refugees escaping crisis--as I said, as an American male I appreciate your sentiment, and I'm actually sure many common Japanese would as well. It's a relatively big country (bigger population wise than European countries) and a few thousand or even x0,000 Syrian refugees would not change things much (though people would definitely bitch about it ceaselessly). Currently, Japan is taking none. However, that is completely Japan's decision to make, and people who can't respect those decisions will ultimately cause more strife than good in the world.
We can push them, but we must respect them. But even in pushing people, we have to be sensitive to context (such as the power relations between the US and Japan, or the West's impirical history).
As a western male who appreciates the same moral view as you, I get where you're coming from-- but as an ethnic Japanese living in Japan, I also know that immigration here on the scale Britain is dealing with would be incredibly disruptive and be a major social burden. Demanding a higher moral standard, and demanding progress is something we must pursue and demand-- but demand it most aggressively for our own country, where we are completely justified to do so. If we were talking about America, I would agree with your 100%-- we need more inclusive and open immigration policy, to be humanitarian and provide paths to citizenship. When thinking about other countries, respecting their own cultures and rate of progress is necessary to avoid committing great evils.
Knowing that I wouldn't wish that on Japan, and not being British myself, I don't see myself as justified on judging whatever decision the British take. By this token though, Brits who are calling the "leave" camp xenophobic bigots are completely entitled to do so. lol
As an economist, I see brexit being a poor decision from that standpoint, but there are values to societies besides economies.