You know, there are many forums with a positive 'reputation system' like I described. These systems are mostly built up on 'thanking' others for their posts. For example, if I write a helpful post there will be a button below that reads "Thank pacific for this post" and a text space below the signature where it says, for example, "User1, User2 and User3 thank pacific for this post". And in everybody's profile you can check out how many "Thank you!"s they have got. This kind of system is actually very encouraging.
What bothers me about negative ratings is this: my previous post got me -3, even though I'd consider it constructive as it adds perspectives to the discussion that weren't there before (even if noone agrees, doesn't matter). Now, I am a person who doesn't care about reputation but I believe there are many on here that would be put off by a -3. And then they would keep from posting things like that again because they don't want to lose rating. But it was constructive wasn't it?
Nobody can doubt the irrationality of the crowd. It WILL dislike some posts for no reason. Members could refrain from posting anything like their previously downrated posts again, even if those previously downrated posts actually were GOOD posts (good posts that were "crushed by "rating trolls"). In effect, those members would refrain from posting good stuff, because downrated stuff can have been wrongly downrated.
This post probably will get me -5, lol.
-pacific