That was war and everyone was afraid of the Yellow Peril.
War on Drugs, War on Terror, War in Iraq, War in Afghanistan, and drug war in Mexico edging across our southern border. To top it all off, Al Qaeda, the Taliban and Latin/South American drug cartels (which American civi gunshops have wrongly been portrayed as supplying) have been well groomed by the media as the new "Yellow Peril."
And overturning a ruling becomes moot once the people are released. However, the Civil Liberties Act of 1988 granted restitution to surviving internees. Reagan signed the law which also apologized to internees.
How does the release of the Japanese, monetary restitution and apology make moot the current existence of intact case law and precedent that says the President can imprison innocent U.S. citizens and foreign nationals?
I think this sort of thing would be more difficult to enact today, and still more difficult to enforce.
All it takes is a sitting president being willing to only have one term (or is already in their second term) to sign such an Executive Order, and the approximately one quarter of the U.S. military (by sampling) willing to execute such an order. You may not have meant it in such a way, but your posting strikes me as sticking ones head in the sand saying "no, it's different now, they would never be able or want to do that." As it sits, there is no current legal obstacle to another 9066 being put into effect so long as it doesn't single out a Protected Class(c).