Problem is, the spooks were not breaking the law -- the government made the laws to allow this. Oh, you think you have to have open public laws? You silly person. These were classified laws. You're not allowed to talk about the fact that you're bound by them, either.
The Yahoo execs would have found themselves in a world of hurt. Why do you think they had to eventually fold and submit to it? Certainly not because they wanted to. It's because their lawyers studied the options and decided that the Feds held all the cards.
Public would have been outraged. The democrats would have had to back off.