There was no Snowden on the Manhattan Project. That was a far bigger effort with maybe 100 or 1000 times more participants.
Programmers get the gift of sovereign status, with all the survival advantages that implies, leakers don't even get a memorial bike rack.
As a former cult member, I know the control The Big Promise has over one's thoughts and actions.
Well, leaving aside Julius and Ethel Rosenberg, remember this was during WWII, where at a minimum, 98% of those participating were in agreement.
In this present kind of endeavor, you'd probably have at least 25 to 40% opposed.