That is the point.
For me, one must consider the source. When the source has a record of mendacity and deception, I am most skeptical of what that source says. When a source is nothing but a propagandist, I tend to reject what the source says as propaganda.
When the claims of a propagandist cannot be proved, I simply don't believe it. When the claims of the propagandist are countered and contradicted by others in the field, the propaganda becomes obvious.
Hersh has provided good sources as to the falsehoods presented by the US government, including several US service members. Yes, there are a few good men in the US intelligence community, and most all of them today are whistleblowers, pointing out the false statements of the US "intelligence" community.
Veteran Intelligence Professionals for Sanity, VIPS, have far more credibility than the CIA or other political branches.
From the military perspective, what possible military advantage could be gained by gassing 12 year old unarmed children in one's own country? Care to take a shot at an answer to that rhetorical? Shall I hold my breath?