If you can’t understand the utility of a social karma system then you should probably ignore all airbnb reviews, amazon, and totten tomato reviews when making a decision, and give them all a clean slate.

It’s hard to argue those systems are not useful if implemented properly. Yes it can lead to prejudice if done improperly, and some prejudice is unavoidable (the whole point of the review is to do a lot prejudging for you to save time) to save on time and effort.