You guys are still arguing with this buffoon?

He's arguing that the system should be secure even if the majority of people are compromised.  There's no way to control that.  If over half the people in the entire US economy conspired to specifically thwart the others, they would succeed.  If over half the computers coordinated to falsify the internet, they would most likely succeed.  But, if you control over half the internet, what's the point of subverting it?

This very fact is what MAKES it decentralized:  The majority controls the system, not some subset/minority of the population.  Not even to mention the fact that 51% would probably be insufficient to overpower the system convincingly, as it's still dependent on luck.