18,000 Japanese-Americans refused to renounce the Emperor or swear allegiance to the United States. And there actually was a quite large Japanese-American espionage network in the US.
But anyway you slice it, the internment (of US citizens) with no specific evidence was wrong. Even J. Edgar Hoover (hardly some civil-liberties bleeding heart pansy) was opposed to it.
All of the great US traitors of the last twenty years...the Walkers, Aldrich Ames, Hansen...have been pasty white WASP guys. Why aren't we interning white guys?
According to this book, USMilINtel had solid information regarding sabotage plans by the kisei (American born and educated in Japan's Shinto schools and then residing in California). There was also the concern that vigilantism against the Japanes in California would reach horrendous proportions. THe result of recently declassified mil documents, the book shows how the issue was not as simple as people have made it out to be.