I think this could backfire. Toxic/trolling comments do not need to be dignified with a response, and requiring one may increase the incentive to write inflammatory posts (assuming that at least some people do this—consciously or not—to instigate reactions).

For well-intentioned posts that are factually incorrect, it seems that there are usually replies that explain the reason for the downvote. When a comment is wrongfully banished to the grey nothingness, oftentimes others step up and defend it. The community immune system functions well as is.

Also, I adore the fade-to-grey side effect of the downvotes. It’s like spritzing a cat with water for scrounging on the counters—an ultimately harmless but super effective reprimand.