What particular biases are you worried about karma affecting? At first thought, I see more reasons why karma would be benficial than not. For instance, someone who proposes many ideas that don't work, and won't update on that evidence would be expected to get a low karma. New people to the community can see at a glance that following their advice is substantially less likely to be valuable than following the advice of someone else. Indeed, following particularly poor advice could easily be harmful, so having a warning would be very important.