I don't know why you think a Moon landing now would be impossible. The tech is there, it's just a matter of $$$$.

The reason a conspiracy would be more difficult is because it would need tens of thousands to keep a secret about it for decades. That includes not just the original fakers, but the scientists studying the (in your theory fake) Moon rocks brought back, the ones using the reflector placed on the Moon, the people running the Lunar Reconnaissance Orbiter which has taken photos of the landing sites, etc.

The Manhattan Project example doesn't help your case: the secret did get out at the time, via the Rosenbergs, Greenglass, Fuchs, etc.