Like most words, these definitions have slipped their moorings over time and come to mean very different things than they once did.
There was a thread a while back on this very topic -- the redefinition of the word "liberal" as a derogation by half-witted writers like Ann Coulter. I'm sorry, I don't recall the name of it off hand. COnservative is also a perfectly respectable word which has been given a bad odor by the dramatization of neo-con imperialism.