Look at the amount of moderation the average Reddit community needs. Everybody is meaner on the internet, people are mean even on facebook just because they don't talk face to face. I remember a woman in Germany who posted that someone should set a refugee home on fire under her actual name, several such cases existed. They obviously all lost their jobs but it shows how maladjusted we are if we type into our keyboards.
I think the difference between extreme trolls and regular people is just to what degree you live online. If you have a regular social life you're probably not that bad of a person online, if you spend your entire day online you end up with 4chan. But I think everybody feels the bad consequences of semi-anonymous or virtual communication.
what do you think the function of parents, religion and society is if not to observe people and watch them? That's what socialization is. Stake in a community and incentive to adjust to social norms, because the consequence of anti-social behaviour is loss of status or punishment.
It's completely rational for individuals to behave selfishly under conditions of anonymity because they face no social consequences. The way humans are conditioned to behave what we perceive to be reasonable is through social interaction and peers, that is to say, to be watched.
The model many people seem to have is that 95% of people under conditions of internet anonymity are good citizens and that the trolls are the aberration. But actually the trolls are just the example of what essentially happens to everyone if they're taken out of what is the natural human condition, which is social interaction including persistent identity and stakeholdership in some community.