If I upvote someone, it doesn't cost me anything, but if I downvote it costs rep and provides a disincentive to do so.
Downvoting is treated also as a personal attack, and there is a general attitude that 'not upvoting' should be the negative way to treat an answer that you believe is wrong or not useful.
I've seen good answers to questions posted later sitting below 7 or so crappy answers with a few votes apiece - the top answer has 40 or so votes, so clearly few believe these to be of use, but due to no downvoting at all, a good answer is buried where no-one will ever read it or upvote it into a place where it will be seen. This contributes to the 'hurry to answer' 'first in best dressed' state of answers, and hides useful material under piles of crap.
So my question is; Why is there both a community and a score-based disincentive to downvote? Shouldn't downvoting be used alongside upvoting to show which answers the community believes is useful, and order them in the reading queue? If 'not voting' should be the default state, shouldn't there be a malus on both upvoting and downvoting?
I'm asking this because I downvote answers, and with rpg.se's ability to check downvotes/upvotes, I often take a look at the ratio - and very rarely is there even a single downvote. Given that some answers receive few upvotes comparatively, or are clearly poorly written or researched, it's clear that downvoting is being preferentially avoided. Why is that good for the site?