Some folks are racist ... It's just that simple.
Some racists hate XXXXXXXX (insulting word fo people with dark skin)
Some racists hate XXXXXXXX (insulting word for descendants of Abraham)
Some racists hate XXXXXXXX (insulting word for people of Teutonic ancestry)
etc...
Naah, it's probably just that the soldiers collecting Japanese skulls and ears in WW II were German-Americans---I think that explains everything... :P