Okay so the conspiracy theory exists so governments can tax the people more in order to fund the "space agencies". What was the benefit in the centuries before space agencies? I'm pretty sure NASA ESA etc didn't exist at the time of Rowbotham.
If the space agencies exist purely to suck up public money that's an awful lot of people involved in the conspiracy, we're talking 1000's of companies that hold contracts with the agencies, don't forget They don't build their rockets, satellites and rovers themselves.
What about all the physicists, universities and other organisations that spend combined millions on research. Are they all in on it too, or are they just stupid?