On The Waterfront is a very liberal film (although Elia Kazan was one of the ones who named names in the Red Scare of the early 1950's). That film and The Grapes of Wrath are probably two of the most pro-union films ever made. Maybe How Green Was My Valley too although I haven't seen that one.

Yes the Golden Age of Hollywood had much more wholesome fare, but not everything was conservative back then either.

Hollywood responds to money; if conservative films continue to make money, they will be made. I think there have been some recent conservative films to do well.