Comic by Penny Arcade
It doesn't work quite like that, but the liberation of freedom to speak your brains on the internet coupled with some degree of anonymity, pseudonymy or even just distance between cause and effect has unleashed a slime-hose of InternetTrolls, CyberHarassment etc.
Don't need to list all examples. But a long time ago, JaronLanier said WeAreBasicallyOK. Boy was that wrong.
Some research which claims the opposite. Anonymity doesn't have much effect.
I suppose one possibility is that it evolved. Initially norms of politeness were stronger and anonymity gave cover for incivility. But as internet speech coarsened over time and we got used to the incivility, people became more willing to do so under their own names.
Interesting and important. Who enables the worst? And why?