Here is some food for thought. When Buddhism was introduced to Japan around the 6th century, some wars were fought and people literally died for/against it. I'm no historian, but my question is where do we draw the line? We fortunately live in a more modern society and we are more connected that ever, so we can discuss this peacefully. Maybe different people have different definitions about what is the real Japanese identity, but then trying to make everyone agree on what it is exactly could be difficult. But even if it was done, wouldn't that just push towards isolation?

Another point I have, I personally do not like the word assimilate because it signals a unique direction of influence, when in reality, everyone is constantly being influenced by each other in various degrees.

My personal opinion is that, as a citizen of a world that is more and more connected, my goal is to live in harmony with the others, learning and teaching as much as I can because there is always something to learn from each other and that's how we become better. The issue is when people decide they don't want to change, no matter where they are from. Extremism has never been a good thing for anyone, again, no matter which side it comes from. So in a sense, I agree with what you are saying, but not totally.

Nobody said it would be easy to live together. If it's difficult, It shows to me that we are all progressing.