In a recent article Cracked dot com has pointed out flaws in several popular conspiracy theories.
The first one I've been telling people for years - that if the moon landing was faked, the Russians would have known and would have made it public immediately.
The second argues that we would see the lizard people ruling the world disappear during the cold winter months - however, I've spent 12 hours listening to David Icke and his belief is not in literal lizards but rather in beings from another dimension that look a bit like aliens.
The next one argues that if Hitler had escaped he would have started a third world war - again I'm not sure this one makes much sense.
The fourth says that if the government were using chemtrails to spray the population, they'd need a lot more planes. This is another good one, given science of aerial spraying. In addition, the idea that you can spray vinegar into the air to disperse chemtrails is laughable!
The next one argues that a flat or hollow earth goes against a lot of the basic science we've learned over the last couple of thousand years.
The last one argues that large scale conspiracies would be prohibitively expensive, and wouldn't take long before someone came forward with good quality evidence. And, of course, we don't see large holes in government budgets and the people who come forward as "whistleblowers" of conspiracies such as 9/11 and chemtrails usually ask us to take them on their word. This contrasts with when real conspiracies have been exposed by whistleblowers such as Chelsea Manning and Edward Snowden, and have been accompanied by a) lots of verifiable data and b) charges of espionage/sedition/etc.