I was just thinking about this particular conspiracy over the weekend - it is a pretty crazy amount of investment, to set up a secret Mars base and ferry people over there.
Dont you think it would be among most "expensive" conspiracies ever imagined? Getting anything off the planet, for starters, is crazy expensive, let alone getting it to mars, let alone building infrastructure there, self-sustaining infrastructure (or you're paying more to constantly ferry supplies) - plus like, solving for all the challenges of Man's first post-earth colony
like THAT was the easiest way for them to do whatever devious stuff they wanted? Why not a base in the Marianas trench? Its a bit closer!