Downvoting is essentially denying someone the chance to have their voice be heard. If it's something egregiously bad, flag it. If you simply don't agree with the statement, leave a comment to hash it out.

We want all information that's not outright wrong or uncalled for so we can get to the best understanding. Downvoting hides viewpoints and makes us work with less information. It also powerfully biases people against a viewpoint, often unjustifiably.

Downvoting would be fine if we all always used strong reasoning in good faith. I don't think that happens for most downvotes.