Genuine question. Why don't platforms support both up and down voting? I've always found it pretty obnoxious that you can only encourage content you want not d

Genuine question. Why don't platforms support both up and down voting? I've always found it pretty obnoxious that you can only encourage content you want not discourage content you don't want. HN seems to have a good system. Shouldn't platforms allow free speech but give the community the tools to discourage destructive speech?