I'm not one of the downvoters in this instance, but actually I disagree with you.
It's not mentioned in HN's FAQ or Guidelines that downvotes are for that purpose, and in fact there's an old comment from pg stating the exact opposite: "I think it's ok to use the up and down arrows to express agreement. Obviously the uparrows aren't only for applauding politeness, so it seems reasonable that the downarrows aren't only for booing rudeness." [1] (It's 6 years old so he may disagree now, but I think I remember him saying similar within the last year.)
On the other hand, it does specifically say in the guidelines "Resist complaining about being downmodded. It never does any good, and it makes boring reading." [2]
It's not mentioned in HN's FAQ or Guidelines that downvotes are for that purpose, and in fact there's an old comment from pg stating the exact opposite: "I think it's ok to use the up and down arrows to express agreement. Obviously the uparrows aren't only for applauding politeness, so it seems reasonable that the downarrows aren't only for booing rudeness." [1] (It's 6 years old so he may disagree now, but I think I remember him saying similar within the last year.)
On the other hand, it does specifically say in the guidelines "Resist complaining about being downmodded. It never does any good, and it makes boring reading." [2]
[1] https://news.ycombinator.com/item?id=117171
[2] http://ycombinator.com/newsguidelines.html