I understand your point, but I don't think it's factually accurate. People have been ignoring Letterman for almost 15 years, but that doesn't keep CBS from paying him over $30 million a year to peddle his garbage.
The people who own, manage and make up the "creative workforce" for the big broadcast networks look at corporate profitability as a secondary concern to hawking their political ideology. If they cared so much about making money, as is frequently used as an excuse about why there isn't a bias in media or movies, then we would have seen more faith-based films like Passion of the Christ, which has earned almost $400 million since it's release.
And yet, we get treated to anti-war/anti-traditional values film after anti-war/anti-traditional values film regardless how horribly they all bomb at the box office.
I agree with you, and will boycott any company who actively supports people like Letterman.