With all due respect to my colleague Partha, the assertion that "These Middle Easterners are being treated like they are for no other reason than where they're from. That's how it's like Japanese-American internment" is completely wrong. Completely and utterly wrong. Had what happened today actually been what happened sixty years ago, the internment of Japanese would have been reasonable. There is nothing wrong with interning enemy aliens during a war. It happened with Japanese, with Italians, and with Germans. What made the World War II internments of Japanese problematic, what made their situation different than Germans and Italians, was that the Nisei and Sansei were interned, as well as the Issei. The relevant orders applied to "all persons of Japanese ancestry, both alien and non-alien."
That's not a semantic difference; that's a real, significant difference. A citizen of a foreign country during wartime should expect to be singled out. Discrimination on the basis of citizenship -- i.e. "where they're from" -- is rational and reasonable (although this particular policy may or may not be). But the World War II internments were not based on "where they're from," but on ancestry. The World War II internments were done by people who insisted on viewing internees as "Japanese-Americans" instead of as "Americans."
That's not what's happening now. Only foreigners, non-citizens, on temporary visas are being required to register. And only those who broke the law, such as by overstaying their visas, are being detained. It's unclear to me how this is "unfair" or "not the American way."
[Update: I see that Eugene Volokh had a similar take on this brouhaha, and on the distinction between this and Japanese internment.]