Initially I had the same reaction. After reading the piece slowly again my impression is:

This is not a conspiracy theory. It is very carefully and lucidly written, with so many details, each of which can be refuted. How does he know about all the meetings between the CIA, Sullivan, etc. Why does no one refute individual facts?

I think he did have a source who provided all this. If the source lied, tough. Investigative journalism is always a gamble. If mainstream media worked, they'd try to press the government on the myriads of claims presented in Hersh's article. Perhaps this would lead somewhere. But the days when mainstream opposed the U.S. government like in the case of Abu Ghraib are over.