When he allowed incendiary race-baiting in his early 90s newsletter, Ron Paul wasn't a bigot (strictly speaking, he wasn't motivated by bigotry). He was a cultist. He belonged to Murray Rothbard's odd little band, and for some reason Rothbard decided in the late eighties that it made sense to do some deep-entry move on the Buchananite/ white nationalist fringe. Why a Jewish libertarian thought this made sense is a mystery, but the guy was weird.
Paul went along for the ride for the same reason Tom Cruise doesn't like psychiatrists.
Update: For those into this sort of thing, Julian Sanchez and David Wiegel have the definitive insider take here. What exactly motivated Rothbard is interesting. What motivated Paul was his lamb-like faith in Rothbard.