That conspiracy theory is not only the most popular conspiracy theory, it is the most accepted, however, it is not without its expert critics:
There are several interviews of various experts in the video above.
Click on the solid button in the middle to begin from the beginning, and go from interview to interview automatically.
Or click on the smaller "<" or ">" buttons to move back and forth between the individual interviews.
Additionally, there is an icon menu at the bottom of the video whereby you can go directly to any one specific segment.
The previous post in this series is here.
Note that historically, secrets can be kept by hundreds of thousands of people for an indefinite amount of time: Daniel Ellsberg.