What are you all going to say when this happens to Rush Limbaugh?
I guess you don't remember the Florida orange juice or the Snapple attempts to do just that. Liberal groups persuaded them to pull their adds with threats of a boycott(and a bunch of misquoted things he said). Rush supporters ran out and drove sales through the roof during the so-called boycott, before the adds were pulled. As I recall, Snapple still pulled their adds, but then when the sales dropped to lower than they were before, they put them back. Rush also got a bunch of new advertisers during that time from people who listened to the show.
Rush has a waiting list of advertisers lined up in case any one bails; not so with Letterman. That said, my basic response is: It’s a free country.