It's pretty hard to argue that the long-term impact of pledge on public television's mission hasn't been corrosive of mission (I've been GM of stations doing pledge for 28+ years). People are voting with their feet -- the number of contributors are down, though those remaining have generally been making up the gap. PBS's ombudsman, Michael Getler, has a column on this that goes into more depth than most that you should read. He includes some telling viewer letters. Link: PBS Ombudsman (print version).
Updated 12:30p PDT. --Dennis