What do you do when you find weird racism in old science fiction books?S

Over at the Straight Dope messageboard, there's a fascinating conversation about the perils of reading old books, especially science fiction novels, in which some very off-kilter racism is tossed out casually. The discussion kicks off with Cyril Kornbluth's "The Marching Morons," in which the main character just randomly hates Africans and African Americans — and then not surprisingly, it turns to H.P. Lovecraft.

All of which makes me wonder... what do you do when you're reading an old SF book and you come across a weird example of old-school, unapologetic racism? Do you toss the book across the room, or just grit your teeth and keep reading? [Straight Dope]