Japan would lose its ethnic homogeneity, but to me that's not something worth caring about or mourning the loss of. The culture would change, but culture always changes.
Have you been there? I can't imagine anyone who has spent any amount of time in Japan would claim there is no cultural uniqueness.
At best, the rate of cultural transformation might be accelerated, but even then I suspect the doomsday scenario of Japan simply vanishing in a generation (or whatever) due to an influx of immigrants is unlikely. If the Meiji restoration or the American occupation didn't destroy Japan's cultural identity then a few thousand more gaijin won't either.
Have you read about Japanese culture before commenting?
Geisha were sex workers with a bit of mystique attached. Similarly, samurai were knights or dukes, and any influence they currently have comes from a romanticised version much like knights received.
Yes, and I understand the difference between history and the cultural perception of it. The ideas these things represent often come from the Meiji period propaganda.
Much of it fabricated by the samurai themselves long after they had to put down their swords and were relegated to bureaucrats. Even the concept of "bushido[0]" has been argued to be a modern anarchronism, and an intentionally Westernized 20th century fiction based on the Romantic ideals of knights and chivalry.