I think that they need to be educated and probably didn't think about who they're hurting by doing this. A little education wouldn't hurt and the best way to do that is email CBS. It's certainly not going to hurt anything and it's anonymous. Raising a public stink about it and merely asking CBS to think twice about allowing tranny jokes on Letterman are two different things.
You cannot force people to become educated about us in one fell swoop. It's a process.
It's a lot better to be mocked and used as the target of silly jokes than to be totally ignored except by pure hate speech.
As Deena pointed out, that's how minority groups enter the consciousness of the people. It happened with Black people before, it happened with gays recently.
It's part of a progression. It's a good sign, IMO.
Writing to CBS about it can be good too. Depends how our protest is stated. It can be a positive input, suggesting them ways to improve in the humour they use with respect to us.
But if we take it as pure confrontation and try to shut them up, it can get worse. They can mock us in a much more negative way, or they can completely ignore our existence.
Frankly, I didn't see it as ill-intentioned. Misguided and ignorant, yup. But that's how it begins, always. It preps the public for a more serious intrusion by "those people" in their lives (as having a TS woman for an interview soon).