Plus, as far as I'm aware there are only two songs by Slayer on the subject, Angel of Death and SS-3, the majority of their lyrics deal with stuff like Satanism (early material) and serial killers (Dead Skin Mask, 213 etc.) so I'd hardly call them Nazi sympathisers, just interested in the subject.
I also love the fact that Tom Araya sings athiest inspired lyrics which totally contradict his personal beliefs