We're talking about separate things, yeah.
The Ainu/mainland distinction is a feature arrived much later than the mixing I am referring to.
My point is that Japan ethnicity is the product of a mixing just as the one occurring nowadays in France, Britain or Norway, between several very different people.
So that, if such mixing produces great results (do we agree that modern day Japan is that?), why not welcome today's mixings for the sake of the great nations of the future?
But I don't think we'll reach a common understanding on this topic, so we can just agree to disagree.
And have a good one.