I wasn’t around then, so I don’t know what the thought process was. But it’s remarkable the resources that were marshalled to accomplish such a task. The entire economy was mobilized to a war footing. Rationing - Americans had to turn in empty toothpaste tubes in order to buy a new tube. There is no way the government would have gone through all those contortions - rounding up all those folks, building internment camps in the middle of nowhere, unless somebody thought it was absolutely necessary. No chance.
That book well covers those reasons.
Leftists have contorted the history in the interest of identity politics. Of course they have.
They lie and/or are ignorant of the true history.