A pure up-rating system has very different results from a up/down-rating system.
With an up-rating system, the ratings are proportional to the number of people who like it (duh).
With an up/down-rating system, the ratings depend on the number of people who like it, and its overall popularity among the general population. In other words, an up/down-rating system results in minority opinions being underrated, and majority opinions being overrated.
e.g. Say I make a wonderful website about tits (the bird). All the bird watchers rave about it and love it. By all rights, it should be #1 search result for people wanting to learn about tits (the bird). But a much larger number of people searching for porn get my site in their search results. They consider it an irrelevant result, and down-rate it. Because they vastly outnumber bird watchers, their downvotes crush the upvotes from bird watchers. And my site drops off the search results radar.
That’s why the bigger sites like Google+ and Facebook only allow upvotes. Legitimately thought-provoking comments and someone challenging the public opinion can get downvoted like crazy because fanboys and the like love to label it as “trolling” and all you end up seeing are the praise posts. Engadget had this problem terribly a few years back, then they switched to Disqus where you can only upvote.
That’s why the bigger sites like Google+ and Facebook only allow upvotes.
Not really. I copied and pasted the OP directly from another site where some people were discussing the subject. Thought it would make for a funny discussion here. I know people have talked about this here before.
You do know that the voting feature on this site doesn't have the same impact or function it does on those other sites, right?