This happens in cyberspace all the time (just look at any HN discussion about airport security): what reason do we have to believe that in meatspace people would behave differently?
Moreover, why do we think that this process would happen in meatspace? Distinction between on-line and off-line is getting increasingly meaningless anyway. People now mostly communicate on-line, mostly get their news on-line, so it stands to reason they'd behave exactly as they do now, only with worse consequences.
No, not exactly. People behave differently when they believe there will be consequences for their actions. I may troll because there is almost zero repercussions to the action online. You see the same action in large crowds. A few people in a large crowd can easily start a riot by realizing their individual actions are not likely to be punished.