Consulting Dictionary.com reveals something interesting. The first meaning is, "Not limited to or by established, traditional, orthodox, or authoritarian attitudes, views, or dogmas; free from bigotry." Doesn't sound all that bad, does it? There must be a more sinister meaning. The second definition says, "Tending to give freely; generous." Again, sounds pretty good. So why has "liberal" become an insult?
There answer, of course, lies at least partially in religion. Bertand Russell sheds some light on the subject with the following quote from Unpopular Essays, "Philosophy and Politics" (1950):
The essence of the liberal outlook lies not in what opinions are held but in how they are held: instead of being held dogmatically, they are held tentatively, and with a consciousness that new evidence may at any moment lead to their abandonment. This is the way opinions are held in science, as opposed to the way in which they are held in theology.
The willingness to base one's opinions on evidence rather than dogma is clearly antithetical to religion. The opposition makes a little more sense now. However, I wish the Democrats would embrace the label.