Disclaimer: I have very little faith in the majority of conspiracy theories. Most are stupid and the people believing in them are even stupider.

These stupid people provide perfect ammunition for malicious governments though.

The advantage of having "stupid" conspiracy theories prevail (such as this one) is that some of the other conspiracy theories that are rooted in some truth can be brushed off as mere conspiracy theories. Governments have little incentive to prove beyond doubt that the moon landing was real as they can use this to hide other things they actually covered up.