Is Seymour Hersh flagrantly psychotic and paranoid?? That would be the kindest explanation of his behavior that fits the facts. It would even be treatable.
Of course, pseudologia fantastica also fits the bill...which is just the fancy name for pathological lying, which (to quote from the link) "is falsification entirely disproportionate to any discernible end in view, may be extensive and very complicated, and may manifest over a period of years or even a lifetime."
Additionally, notice from Greyhawk's post how Hersh appears to be completely indifferent to the potential lethal consequences (to others) of his malignant behavior? This is rather typical of the paranoid, who often displays a rather cool grandiosity and sociopathic indifference to others.
Is it any wonder that this fruitcake (who calls himself a journalist) is a treasured source of "factual" information for the proud political left? Is it any surprise that the Latin word for left is "sinister"?