Ethnic prejudice will always be with us. The mayor whose controversial statements are the subject of this article comes from Japan's subhuman class, the burakumin. FDR, along with the majority of Americans of his time, undoubtedly saw the Japanese he interned as subhuman. The difference with the Germans is that they attempted to kill every last one of the people they considered subhuman, along with everyone they thought might have just a smidgen of subhuman blood. The Japanese never tried to exterminate the Chinese. They targeted hostile regions with chem and bio-weapons, but these were populations they would have attacked with conventional weapons, anyway.
FDR didn't like the Japanese, that's true. Nor did he like the Germans. He was a Roosevelt, and Theodore Roosevelt didn't like the Japanese or the Germans either (Teddy was screaming against "the Hun" practically the moment World War I began).
Both Roosevelts were interventionists with regard to both the economy and foreign policy, yet because he was a Republican Teddy is considered a "jingo" and a super-patriot, while FDR is considered a traitor and an "internationalist."
You make a good point about Japan merely doing what the West had done for generations. However, most of those Western nations eventually came to abjure their former behavior. Japan's behavior during World War II--not its going to war, but its behavior during the war--is unjustifiable. However, I recognize the fact that during this "ethical evolution" some countries were frozen out of the colonial adventure while the nations that came to be "enlightened" nevertheless kept all the colonies they had won by similar means. I recognize the hypocrisy, but this doesn't justify the Rape of Nanking or the Bataan Death March.
I hope you understand that I am not anti-Japanese (there was a time when I advocated rearming Japan myself). I also support them against China (a nation entering on the same rapacious path but which will never be called on it due to its nominal "Communist" status making it immune to liberal judgment). I just recognize that there are always unforeseen consequences. A reawakened Japanese militarism combined with historical revisionism is not a consequence anyone wants.