I understand why Muslims do, since this concept is repeated many times in the Islamic texts (for instance it says "don't take Jews or Christians as friends", and among Mohammad's last words were "may Allah curse the Jews and Christians"), but why do Nazis and the KKK?

Please comment....especially why in today's modern, civilized world, they still cling to those outdated beliefs.

(I personally know plenty of Jews, and have nothing against them whatsoever.)