Earlier quoted context omitted.
Upvote = I like this. Downvote = This is noise/off-topic/abusive. Thats the way it should work, and is part of what makes HN different to say Reddit. In reality, its becoming increasingly common for people to downvote something simply because they disagree with it.
Then upvote/downvote are the wrong semantics for what you are proposing. Change them to "like" and "spam". For a multi-lingual audience, that is easier to grok than to hash the up/down arrows.
Edit: Would whoever downvoted this care to explain why? I'm genuinely interested.