I don't believe the story about the Guy who Snitched on the Occupy Wall Street protests...I have a different theory...
I think there is a much simpler explanation, that we're not supposed to figure out, because if we do, we can route around the damage, which would tip the scales towards justice, and we can't have that now, can we?
How about Carnivore?
How about the secret rooms at the Telephone Company offices?
The Onion (which is a satirical publication)... has the best illustration of this in their story about the CIA funding Facebook.
(Update) - I think they simply scan everyone's communication for keywords which indicate dissent, and then dig in closer... it's quicker and cheaper, and more effective than random human offers of information.
Total Information Awareness is what they used to call it...
If my thesis is correct, and this is the result of monitoring and not human factors, instead of just mis-trusting each other, we simply need to encrypt our communications, and prevent this system from working against us while maintaining its advantages of quicker communication.
It's a theory... and words are cheap... take this with a grain of salt....