No reputation or information is a recipe for meaninglessness; as a reader I have neither the time nor the tools to fully evaluate every statement ever made to me; I must use heuristics to aid my reading (e.g. I will almost certainly ignore anyone who claims the moon landings were hoaxes; it's not worth my time to investigate his claims).
I'm actually very excited by the idea of anonymous reputation, as it could enable all sorts of the things needed to have a well-run global network without enabling physical assaults on persons.
For trading pseudo-anon there is already this reputation system which has worked well http://bitcoin-otc.com/trust.php
Not true. We do not need to accumulate reputation to have a meaningful conversation. For example, I've seen informative conversations on Secret with the only identity mechanism being the icon they're assigned (presumably at random per thread).
Edit: I also don't recall usenet having a mechanism that 'kept score'. Slightly before my time so I may be wrong about this.
I'm not talking about "keeping score" in a system. I'm talking about the ways human handle identity and associate properties with objects. I may not see your karma, but I see your nick. I don't know your name, or anything about your life, but I know your nick is a reference a person somewhere. If I keep seeing comments written by user amirmc that stand out because of their clear argumentation and reasonable tone, I start to recognize the author and accumulate a feeling of respect. So the next time user amirmc disagrees with me, I treat the arguments with little more care and consideration than usual, because I recognize author as a reasonable person.
This is a natural mechanism of human interaction. My point is that if we reject the entire concept of identity, we will lose a lot of information vital to evaluating an argument.
Yes, they probably can't find out that the 10k-karma-guy is Jack Miller, but all readers of his posts will be influenced by the 10k-karma.
HN hides the karma mostly. But SO shoves it right in your face, that some gold-20k-guy wrote an answer.
Also people will vote stuff up because they like it. This may be because it's high quality, but it doesn't have to.
Within forum post culture there's a built-in tendency for content to be fast and disposable. This makes identity relatively more valuable, because it allows a stream of posts to be put in context, just like with a book.