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> I was always of the impression that short low-quality comments that don’t further the discussion are prime examples of acceptable downvote targets here. Disagreeing with a constructively expressed idea is best done by expressing your own argument in a reply.

Amen to that. Not how it always works around here though.

They are not, the guidelines are linked in the footer and don't mention anything about downvotes aside from "not talking about downvotes".

https://news.ycombinator.com/item?id=16131314