Can't speak for him, but I haven't. And I know others that haven't. Doing so only reflects an insecurity in your own opinion. I downvote for ad-hominems, or blatantly (easily verifiable) false claims.

Assuming that others downvote over differing opinions does paint you in the light of doing that yourself, though...

The downvote button isn't a disagree or dislike button. If I disagree (and care enough), I use the other button, reply, to try to understand their point of view and try to get them to understand mine.

The forum founders have stated that the downvote button is for disagree/dislike. If you think a comment is very bad, there's a 'flag' function if you click on the comment's timestamp (if you have the requisite karma).

My understanding was that downvoting was for comments which do not contribute to the conversation.

I'm both surprised and sad to hear that the downvote button's intended purpose is disagreement. This seems like it would discourage people from posting alternative points of view if their view is the minority.

As much as I tried looking for it on my own, I couldn't find one, so would you mind posting a source as to where the founders stated the purpose of voting?

I found this, but it's clearly Unofficial

http://jacquesmattheij.com/the-unofficial-hn-faq#downvoted

That said, the author currently has karma 111515 so he likely knows something about it.

The guidelines[0] do mention "Please resist commenting about being downvoted. It never does any good, and it makes boring reading." [0]: https://news.ycombinator.com/newsguidelines.html

From pg: https://news.ycombinator.com/item?id=117171

That... kind of makes me want to visit this site much less.

I often upvote both sides of a polite to-and-from between two parties with differing opinions, if the discussion is interesting, since that, I feel, adds to the quality of the whole page. I frown upon learning that it is encouraged to downvote if you disagree. Isn't it an equivalent of childish sticking fingers into your ears and hoping the other opinion goes away?

I usually try to argument with them, that's what a discussion is about, a exchange of argument and a test of there validity. Everything else, is just bubbling oneself into another ideology.