How about something not seen until fairly recently? The reply button. In the UK for instance, there is hardly a single newspaper or online magazine that provides this in their 'respond to article' facility. You can post a comment but without a reply button no one can specifically challenge that non-sequitur or unsupported abuse you've churned out. They can do it indirectly by naming you but who's going to take the trouble to refer back? Where implemented, I'm sure this facility has had a positive effect on the way people treat each other on the net.