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Derren Brown produced an excellent show about this kind of phenomena. He reasoned that people lose their decency and inhibitions and act like morons when they can act anonymously in a crowd.
This is why perfectly nice, ordinary people troll online and why normal people can get involved in football violence.
He set up a fake gameshow, and everyone in the audience had to wear a mask over their face. They made decisions that affected a guy sitting in a nightclub who didn't know he was surrounded by actors. For example, they could either vote for a hot girl to flirt with him, or a muscly guy to accuse him of looking at his girlfriend and start a fight with him. It ended with the entire crowd shouting and cheering as someone broke into the guy's house and smashed his stuff with a baseball bat.
It was called "Derren Brown: The Experiments - The Gameshow". If you're in the UK, it's on 4OD. If you're outside the UK, I highly recommend you try and get hold of this show and watch it.
I'd agree fully that the feeling of anonymity lowers inibitions just like the drink and people suddely feel they can behave in ways they would never behave normally. It is the "Liquid Courage" of modern communication. We used to see lots of Keyboard Courage in the old BBS scene that preceded the popular explosion of the Internet scene. It can be seen in archives of the Usnet and other early mailing list forums.
I think people will generally exploit any medium that provides a sense of anonymity or abstraction from face to face conversation.