Well as I recall it there was a Congressional Committee which investigated MK Ultra, during which they made findings of fact and ordered it to cease and desist .
Like many things which you can prove I think many people ignore it if they're subliminally instructed to regard it as a "conspiracy theory" by the BBC and other outlets. If they witnessed something themselves but were told that it didn't happen they'd insist that it was a conspiracy theory in order to identify with the " intelligent" people who " know the truth".