Just a comic, but there is something to this. I think it comes down to what you see as an exception and what you see as the rule. Carol might be the "good exception" for them, while "ThE mEXiCaNS!," in general, are evil and eat pets or whatever. Maybe Carol was even the "I'm not a racist, my friend is mexican" friend.
I even have people in my life (not that I chose to) who are immigrants themselves, came to my country for economic prosperity, and now hate new immigrants.