Negative externalities.

I am aware of the concept. What exactly do you mean?

The above study is sufficient evidence for me

It says "This paper investigates how ratings on a piece of content affect its author's future behavior." I don't think LW should be in the business of re-educating its users to become good 'net citizens. I'm more interested in effective filtering of trolling, stupidity, aggression, drama, dick waving, drive-by character assassination, etc. etc.

It's not like the observation that downvoting a troll does not magically convert him into a hobbit is news.