That's true, no one has to. But FDR was, and he and the (Arabist) British foreign service wouldn't let them into Palestine, either. So their boats foundered, or they were turned back to Europe and were killed by the Germans.
At the same time, liberals (who may not know they got their talking points from the KGB) are all over Pope Pius XII for "not doing enough" to help Italian Jews, when in fact he personally set in motion a campaign to hide Jews in Italian convents and seminaries and get Italian passports for tens of thousands of them. Between one measure and another, it's estimated Pius XII saved 490,000 Jews. The Chief Rabbi of Rome converted to Catholicism after the War, and took the baptismal name "Eugenio" (the Pope's given name) in his honor.
I actually don't fault Roosevelt for sequestering the Nisei, a percentage of whom really were security risks—or rather, their Japanese-born parents and grandparents were (according to memoirs I've read by Nisei). But he really was a maniac who acted as if he had no fear of God.
And the Brits were not particularly at fault for denying them entry. British imperial rule rested on the most tenuous of threads - the belief among the local populace that London's rule was preferable to the alternative. Introducing large numbers of Jews into the Palestine Mandate had the potential of making British rule not just there, but everywhere a large Muslim population existed untenable, on the eve of a potential shooting war with the biggest economic and military power in Europe, Nazi Germany. Again, like FDR, British leaders had no obligation to let large numbers of Jewish or other refugees into their territory, whether Britain proper or British holdings around the world.
I'd say that was racialism. It's one thing to intern individuals born abroad or even the first generation born stateside. They were interning individuals with 1/16 Japanese blood, which is to say they were interning the great-great-grandchildren of the original Japanese settler stateside.