His reports about the intial actions in Afghanistan were so absolutely bogus as to belong in the fiction section of your local library.
You can't defend them. Don't even try.
Why you're even here at this forum is puzzling.
You may be referring to a flap some years ago over documents about JFK. Hersh's book on JFK, the Dark Side of Camelot, came under fire from Kennedy loyalists even before it was published. They challenged Hersh's supposed acceptance of disputed documents about Jack Kennedy, which was taken as indicating that the book would be unreliable.
In the end, Hersh did not use the disputed material in the book. Nevertheless, the attack diminished the force of the book, even though Hersh had some embarrassing new revelations about JFK. Most reviews mentioned the controversy, recycled the Kennedy loyalist allegations against Hersh, and took a critical tone toward the book.
Hersh is a left-winger, but he is also an energetic and at times capable investigative reporter. I think that he did a flawed but interesting job on JFK; but it is an investigative effort, not a history.
Here are couple of reviews on the Dark Side of Camelot. The first (Ed Epstein) is more credible than the second.
http://edwardjayepstein.com/archived/hersh.htmhttp://www.assassinationscience.com/wrone2.html
There is a trick of sorts to reading investigative and analytical reporting. Read it once for effect, then pick out the hard and well-sourced facts. The rest is opinion and guesses, usually from people who have an ax to grind or only a small view of the issue. Often, the unnamed sources are not so much whistleblowers fearing retaliation as people so discredited that it is better not to name them.
Most of the time, when closely read, Hersh and other such reporters depend on conditional terms like "might" and "could" and "in the opinion of." They may be correct, but they are further from hard evidence for their conclusions than they pretend to be.
I was not impressed with Hersh's Abu Ghraib story. There were a lot of gaps, unnamed sources, and unsupported assertions. I don't think that Hersh's story is going to develop much further than it has.