20 years ago, the fight would have been over and Letterman would have won. Things change.
Culture changes by degrees and generations.
I think that O'Reilly and Hannity and Limbaugh, are for the most part, pompous self-serving windbags. But, I am glad that they exist to provide a counterpoint to the multitude of liberal pompous self-serving windbags that dominate the mass media. OTherwise, the conservative view would be completely lost.