Well, no. Companies are also accountable to their customers and to society. If they were dumping large amounts of toxics into rivers, that's something society has a stake in and where the company is accountable to it.
If Twitter were to sell access to protected updates, that's something their users need to know. If they were doing so illegally, that's something that society must know.
It all depends on the information that will be revealed whether or not it's ethical. I'm inclined to not give an "unethical" verdict too quickly. TC is at least caring about individual persons that may be damaged by the revealing of some information.
Govt comparisons fail -- this is Twitter. Dumping toxic waste comparisons fail -- this is Twitter.
Likelihood that Twitter is organized enough to sell access to private messages, or any actual saleable product? Extremely low.
With that said, I still can't help but be curious. It'll be interesting to see how all of this plays out, and if some of the documents do end up released to the public, I'll probably cave and check up on the juicy tech gossip.