The issue of abusive behaviour and harassment online seems to keep getting worse. The problem is often blamed on anonymity, and on the face of it, that sounds like a plausible explanation. After all, where's the incentive for people to behave in a civil manner if they can hide behind a fake name?

He compares anonymity to wearing a mask. "People with masks do commit theft," he says. "But when we think about social norms we're asking…'would putting on a mask cause people to become thieves'? If you or I were to put on a mask, or become anonymous online, what would that do to us and the way we treat other people?'"

If you think that the community you're participating in is one where it's ok to insult people or threaten them, then that's what that social norm is.

The social norms of a person's online community shape what's considered acceptable behaviour.

"If you think that the community you're participating in is one where it's okay to insult people or threaten them, then that's what that social norm is," Nathan argues. "Those social norms apply whether or not someone is identifiable or not."

Nathan points out that in the US, fully half of people reporting online harassment say they knew who their harasser was.

So, why don't the trolls stick together and leave the rest of us alone? Trolls, harassers, and bullies don't exist in a vacuum. "When we come together in discussion threads, when we interact with people [online] we carry the norms of other communities with us."

We can't design the problem away. Nathan thinks it requires "actual social change". But designers of online platforms can do things to help reinforce social norms. For example, they can post community rules to the top of a discussion page, a strategy Nathan and his colleagues tried in a recent study.

"That's a great example where we changed something about the design of a community," Nathan explains. "But that only worked because the community already had strong norms against harassment, against hate speech, around people staying on topic."

Read Nathan's full blog post here.