In 2011, a Reading man was jailed for raiding the Facebook tribute pages of a 14 year old girl who had committed suicide, filling it with crass jokes and insults. He had never met the girl in question.
That's an extreme example, but it's a phenomenon almost as old as the internet itself: trolling. Examples of trolling range from the above to the extremely mild winding up of people to draw a reaction. Even outside of trolling though, discussions routinely turn into arguments that often turn personal. Are people genuinely more aggressive, rude and unpleasant online, and if so, why? And what can we do to counter that, and make the internet a more tolerant place?
Common wisdom dictates that people are more aggressive, rude and forthright online because they're anonymous and can act as unpleasantly as they like without immediate consequence. If you're irritating in real life you risk at best social sanctions and at worst a physical assault. There's definitely evidence that points to anonymity as a factor, especially in the internet's early years when IRC, Usenet and message boards were the norm, but nowadays Facebook commenting has added a personal touch, seemingly without significantly curbing the aggression.
Netiquette - http://www.studygs.net/netiquette.htm