Here's a friendly suggestion for a slightly different policy. (I didn't vote up or down on your comment.) I upvote, first of all, whenever I see something I learn from or think that other people will learn from. I especially upvote new submissions that I think will help the hacker majority here learn about facts about the real world that aren't usually discussed in the hacker monoculture. As mentioned elsewhere in this thread, I especially like to upvote comments that ask follow-up questions looking for more information, especially those that take advantage of the hypertext nature of the World Wide Web to ask for links to more information to back up someone's statement about one issue or another.

My downvotes indicating lack of adherence to the guidelines or bad impact on the community expand to include downvotes indicating disagreement when

a) the comment to which I'm responding doesn't leave a good opportunity to be replied to by a comment,

and

b) the comment itself is repetitive, a mere declaration entirely unsupported by evidence, or flat-out in disregard to a more thoughtful comment that has already been posted to the thread for a while.

My goal is to upvote a lot more than I downvote. (But since I don't have statistics on my own behavior as a reader of HN, I don't know if I am achieving this goal.) I see a lot of statements that I disagree with that I just let pass. Statements that I disagree with have to be actively annoying, by the criteria above, for me to downvote. And people can disagree with me factually, even proving me wrong by specific evidence, and I will upvote that if I have learned something from the comment.

P.S. I wonder why there are so many more complaints about too many downvotes than about too few upvotes? I rather think that not upvoting the really good stuff here is the main problem.