[Arch0wl]

Labeling people 'retarded' can be a powerful device when done properly because it is a negative example. It does nothing to persuade the person you're debating with, this is true. But unless this is an issue on which many people will have already made up their minds (abortion, for example) it's likely that not everyone reading you has, in fact, made up their minds. They're looking for a "side" to join. And if they see someone being called retarded, they have to face the strong possibility that if they join that side they, too, will be called retarded.

On the internet though, the dynamic is a bit different. Forums put most people on equal footing, so it usually doesn't work very well. It only works if the authority of the "retard" label is greater than any authority which might oppose it. So usually, you either need a chorus of people calling someone retarded or an extremely authoritative voice (a professor among students, for example) to deliver the "don't be like this retard" blow.