Gil, I am unsure whether there is a language misunderstanding here and so I will first clarify, in case you have not understood me.
I am not saying that the argument is the only one with any merit BECAUSE it is the only one consonant with American values; I am saying that the argument is both the only one that has merit AND the only one consonant with American values.
Now, the following response is appropriate if indeed you have NOT misunderstood me:
I think that if you believe there is merit in the position that Japanese Americans needed to be interned during the war, you should set that position out and explain why; the exercise will demonstrate to any fair-minded person that there is no merit in that position. But I will caution that, in my experience, when people do take that position, they expose themselves as being absolutely morally bankrupt or, at best, like FDR, overly trusting in people who are morally bankrupt; and it is very, very difficult to image how one can take that position without being so.