There have been efforts to build reputation systems that don’t rely on central servers, like early day bitcoin’s Web of Trust, which allowed folks to rate other folks with public key crypto, thus ensuring an accurate and fair trust rating for participants, without the possibility of a middle-man putting their thumb on the scale.

One problem with it is that it was still perfectly practical for bad actors to accumulate good ratings, then cash out their hard-earned reputation into large scams, such as the “Bitcoin Savings & Trust” (for $40 million in that particular case), which quite possibly made it measurably worse than not having a system that induced participants into making faulty judgments in the first place.

I think the main practical value of something like reddit’s karma is an indication of age and account activity, both of which can probably be measured in other, if less gamified ways.