Ignore YouTube and 4chan's /b/ board for the moment. If you look at some of the communities at reddit, for instance, there are subjects that are discussed thorougly which would never see the light of day if their authors had to appear before their friends with their full name and picture. Some of these discussions have shed light on parts of humanity and human nature that I would have never known about if it wasn't for anonymous internet forums. For instance interviews with psychopaths and murderers, mean stories about ex-girlfriends and boyfriends, candid and unpainted interviews with sex workers etc etc etc. In general, the stuff that doesn't come up in polite conversation and everyone pretends not to be associated with. Some of these discussions have changed my views on both political issues and more mundane things. All because someone is suddenly allowed to broadcast forbidden stories to a large crowd. And people are allowed to comment on it without fear of being judged or socially persecuted.
The difference in the style of comments on Facebook and reddit perfectly exemplify what happens with civil discussion when people are allowed to be anonymous, and the huge difference in behavior and mindset that this causes in Western society. It is a pretty big deal.