I'm not sure whether the internet has revealed a whole new level of misbehaviour or whether it is just making current levels a lot more visible, at least to us all being so connected via social media.
The average person is utterly horrified by the behaviour of a few on the Internet. People's biggest fear online seems to be that they'll be exposed or ridiculed, so it is one of the only forums where we can see unbridled human emotion and interaction with no social etiquette governing its expression
It may be that the punishment for doing so is less severe - or easier to avoid. Being able to sit behind a monitor, anonymous and removed from the wider public gives people more apparent courage than they might have in person.
Video games provide a key example of how this anonymity can apply. If you were hit by somebody in real-life, you would be able to fight back and protect yourself - even if the punishment was minimal, there is the immediate consequence of having been attacked backed up by laws and regulations that people are signed up to. On or offline. But online, some players will face no such consequences for their actions and abuse others without any apparent repercussions - they simply threaten worse consequences than actually exist while hiding behind pixels on-screen (or avatars).