Not paranoia at all, any more than other measures taken in time of war.
Hitler was doing ethnic cleansing and committing genocide. Don't use that as a facsimile of the Japanese situation.
We can look back 75 years later from the comfort of our computer desks and exercise the new political correctness now but at the time America was fighting for survival against an enemy that at times, threatened to literally invade our homeland.
I think one can argue that this applies today at the southern border. By your logic we should also be "paranoid" against americans of Mexican descent as they may have loyalties to Mexico. Again, dont understand your logic but then again I dont care to.