Historically, US immigrants have been able to assimilate time and time again. That isn't the case in Japan. There are Koreans who's families have lived in Japan for hundreds of years... yet they still aren't considered Japanese. The Japanese would rather rely on robotics instead of immigration to mitigate their problem with a dwindling population.
Yes, the US has done some horrible things in the past, yet:
1. we publicly admit them in the historical record
2. we teach these mistakes to our children in our schools as both reminders and ways to avoid them in the future.
