> If you have a deadline and won't be getting new resources any time soon, and what purpose does a estimate serve if you are already committed?

I didn't commit, the sales person did. I'm not in trouble, he and the company is. I can just leave, it is their fault if they make bad deadlines. The only reason they can continue is that engineers don't push back and quit when it happens. You work hard so that the sales person can get his juicy bonus, why should you do that?