Twitter as a private company can moderate content as it sees fit. But the government is supposed to be constrained by the First Amendment. And here, they technically are, because they're not forcing Twitter to take action. But there's always the background threat of regulation if Twitter doesn't play nice, so it's not as black and white as this.
Having been on the receiving end of such requests I was pretty happy all of them were made in a confidential manner, it saved everybody a ton of headaches and reduce the amount of grip the various miscreants had on our community. Doing that in the open would have caused massive issues, some of these people were downright dangerous and others simply needed help, keeping their data and our interaction around that data confidential was - in my opinion - a good thing all around.
Just look at COINTELPRO for the most egregious example.
Then there's Waco, Ruby Ridge, the campaign finance corruption, infiltration of latin American governments, and modern operations similar to COINTELPRO to take down various movements like occupy wall street.
They are a mafia, not some benign group that can be blindly trusted with secret carte blanche powers.