I believe this predates the internet. I can't remember the study now -- perhaps fellow HNers can -- but there is a study where they asked a group of people to

I believe this predates the internet. I can't remember the study now -- perhaps fellow HNers can -- but there is a study where they asked a group of people to take a side in a debate. The debate was structured so that it sounded like A was the intuitively better choice, and when polled almost everyone agreed the group would support A. One plant was armed with excellent arguments for B, and when presented with these arguments, the group switched to supporting B. When asked later, they thought they had supported B the whole time.