One thing I haven't seen mentioned here (or even on Reddit) that I think is the most sinister effect of a downvote button is that (at least on Reddit, I'm very new to Snapzu) it meant that all content had a 50%-70% chance of being buried forever, regardless of quality. How so?

Well, first of all you have filters. In general when content drops below a certain threshhold it stops being visible to users. Either through a hard filter that hides the content, or it simply falls beneath users' mental radar. Which meant that when you submitted content to reddit it had a few LIVE OR DIE minutes to garner a few upvotes or it would simply be buried by other content. If at any time during those crucial few minutes it received a downvote, it was essentially gone forever. It would drop below 1 karma and never be seen by another user. For all the talk of democratizing content, reality was that all it took was ONE downvote to bury a submission forever. Pretty brutal if you ask me.

Add to that the culture of "knights of new." (A culture that makes my stomach churn.) People being praised and heralded for ruthlessly burying content. An entire culture that lionizes the burying of content. Couple that with the fact that a single downvote is all that's required to bury something forever, and you get a site where it's almost impossible for good content to flow to the top unless it's a repost or submitted by a "Power" user. Which, as we all recall, is what brought the Digg empire crashing down.

A downvote button is, in theory, a great idea. It means "this is irrelevant or offensive, nobody should ever see it." Unfortunately large groups of people can't be trusted to use it responsibly and it invariably turns into an "I disagree" button. Which then creates an environment where good content cannot float up. I'm vehemently in favour of anything that banishes the "I disagree" button.