On the Fact that FDR Knew (Through Multiple Investigations by J. Edgar Hoover, John F. Carter, and Francis Biddle) that the Vast, VAST Majority of Japanese-Americans Were Honest, Patriotic, and Law Abiding Citizens and STILL He Denied this Entire Ethnic Group the Most Basic of Civil Liberties (Most Were Charged with No Crimes and Delivered to Remote Compounds that Were Surrounded by Barbed Wire and Manned by Sentries with Machine Guns)

He did it for political reasons. He needed to carry California and other Western states, and what better way to do that than to appeal to the virulent anti-Asian bigotry which by then had permeated the whole region? Not that the dude necessarily needed any extra incentive, mind you (his seemingly ingrained hatred of anything Japan - the fact that he didn't persecute citizens of Italian and German extraction, the fact that he had wanted war with Japan as early as 1933, etc.).