downvotes on HN are, by official policy, for disagreeing with ideas. They are not just for low quality posts. And, even on sites where downvotes are supposed to be for low quality/off topic, etc enough people still use them as "I don't like this idea and don't want you to spread it even if it's arguably valid".

Further, they're a form of violence against the poster. Not sure what other word to use to be told in a single click "You Suck!". It is or arguably can be a form of bullying.