This argument only works if you believe that there are enough people who understand the complexity and nuance within the system at a level sufficient to understand it.

It goes back to the design of DES - the NSA influenced small design changes in the SBoxes that had implications that only they understood. This gave an advantage, even though the algorithms were completely "open source".

http://en.wikipedia.org/wiki/Data_Encryption_Standard#NSA.27...

In that case, they made the encryption STRONGER. But they certainly showed how that type of influence could happen.

I don't happen to be enough of a conspiracy theorist to believe that they're messing with Tor - there are better ways, especially when a vast majority of the traffic isn't through Tor.