Media and the mainline
Check out this graphic from media matters if you want to see the significant voice that religious conservatives have in the media in juxtaposition to progressives.
What is also interesting is that if you look at the progressive speakers, few represent the mainline protestant tradition. It'd be interesting to see how many mainline leaders are asked to speak on matters of faith and theology, not just politics.
Of the list I recognize Jim Edgar from the Nat'l Council of Churches and John Thomas, who heads up the United Church of Christ. Lots of reasons for the public perception about religion and Christianity in particular, but the media coverage certainly plays a part.