Okha,
Thanks for sharing about your father's experiences. His experience with the German-American machine-shop owner is interesting. Yes, given that some Americans of German extraction were also interned during the war, the owner should have been more sympathetic however this was not the case. One reason, I think, is that German immigration to the US had gone on for much longer than Japanese or even East Asian immigration. Germans were a presence in America from colonial times. As I recall, the American colonial legislatures in the 1760s once only narrowly decided to maintain English as the colonial lingua franca instead of German as, in some areas, German settlers neared the numbers of those from the British isles. Another reason is that, obviously, German migrants were viewed as being members of a wider European civilization by the Anglo-Saxon establishment in America - even during world wars I and II. Japanese were viewed, by more established native-born Americans during that time, as part of a lesser-known - and hence more threatening - cultural "other." Add this, even before 1941, to the increasing geo-political rivalry between Japan and the US and you have Americans veiwing Japanese immigrants with alot more cynism than toward German or Italian emigres.
True, Germans were interned but very few relative to their numbers in the population and most of those so jailed were conspicuously political and were frequently active in the American Bund or the neo-fascist Silver Shirts. Additionally you had the problem of numbers. So many Americans had some amount of German-blood that a comprehensive program of internment such as happened to Japanese but directed towards German ethnics was simply unattainable had the desire even existed. Had such a program been carried out, the Feds would have been interning most of the population Wisconsin and the Dakotas!
Nikkei, by contrast were mainly concentrated on the West Coast in 1941 and their cultural and physical differentiation from Euro-Americans meant that they were more easily identified as threats and targeted for internal exile.
Despite all this, it is interesting that the justified compensation reward paid to Nikkei internees and their next of kin in the 1980s was not also paid out to German and Italian internees. While European internees, as I indicated, were far fewer than those of Japanese extraction, there is no reason they should not have been compensated as well. Many ethnic German US citizens suffered privation as well. Neither have the Aleuts of Alaska been compensated for being forcibly moved during WWII to get them out of the way of advancing Japanese forces in 1942.
To address the question of justifying racial or national animosity, I think it is just human nature not to want to acknowledge or dwell on bad things done by your own group and instead refer to acts committed by other groups, particularly as those acts affected your own group. Hence the ethnic German disliking Japanese-Americans due to Japan's treatment of POWs and his silence on the holocaust. Not that the guy, simply by being being German was in any way culpible for German atrocities any more than your father was culpible for Japanese atrocities because of his ethnicity.
My point is that each of us, as a member of some community, real or imagined, prefers to remember our strengths or when our group was the victim and not the un-edifying parts of our history when our group attacked others. Germans prefer to remember Dresden but not Auschwitz, Jews prefer to remember Auschwitz but not their role in the Bolsehvik Revolution or the dispossesion of the Palestinians, Japanese prefer to remember the Tokyo firebombing and the atom bombs but not the Sino-Japanese war or the Thai-Burma Railway, British people recall the Blitz but not the shooting of un-armed Indian protesters in 1919. Not taking sides, just saying that that is just a part of being human.
Best,
Gunnar