and
While it may be one thing to rationalize Andrew Jackson's campaign to eradicate the Indian or our ill-conceived perpetuation of slavery (until it was good business to free the South's, if not the North's, slaves upon secession), it's clear that this bent was extant during World War II.
Anyone who's got any worries about whether or not the US as opposed to Pius XII was terribly worried about Hitler's reduction of Jews, Catholics, disabled, mentally deficient or otherwise Unwanted should listen up to the words of President Roosevelt. He and his "Healthy Babies ONLY" March of Dimes buddies being the US's smiley face eugenicists par excellence and far more cuddly than their blueblood brethren at Yale or Cold Springs Harbor.
President Roosevelt made his contribution to the on-going dialogue concerning Puerto Rico's "population problem" by jokingly telling Charles Taussig, his advisor on Caribbean affairs, "I guess the only solution is to use the methods which Hitler used effectively." It is all very simple and painless Roosevelt said--"you have people pass through a narrow passage and then there is the brrrr of an electrical apparatus. They stay there for twenty seconds and from then on they are sterile."
So ... given the ill-thinking already pervading our government in earnest, given our weariness at the close of the war ... I don't think it was exactly a giant step to succumb to certain pressures to just eradicate the Japs and -- like Saddam and his Soviet buddies in the Gulf War -- get a little bang for your "hopeful research" buck by testing your nukes, if not your bio-weapons -- in the meantime.