IIRC it came to light when documents that were supposed to be shredded were declassified by mistake. The government has shown that it's actually really good at keeping secrets, or at least keeping things quiet. Elsewhere in this thread there's the discussion of a possible FBI program to get people to commit mass shootings that's widely considered to be a crazy conspiracy theory despite there being individual documented examples ie https://www.cnn.com/2017/11/29/politics/aby-rayyan-fbi-terro...

My whole thing with MK-ULTRA and Ted is that researchers were happy to do stuff as damaging and way less (potentially) useful than his experiment.