Like it or not, downvoting is often perceived as an act of social violence by the downvotee. And it is intended and widely understood to be a punishment, the op

Like it or not, downvoting is often perceived as an act of social violence by the downvotee. And it is intended and widely understood to be a punishment, the opposite of approval. Social sanctions like that may be necessary, but they also degrade the quality of life overall. Downvoting should have a cost, especially when it's an anonymous act.