This is a really good question, and might not be as simple as first glance might indicate. 
The short answer is there is no system that will remove all harmful biases. The very metrics we use to prevent one visible bias will strengthen another, or multiple others we don't see yet. 
The screening process and validating the "best" answers is the best solution we, as people, have for now.
Silencing the bias we don't like tends to drive it underground, unseen and mutating, into something much worse.
spam fails_task lang_mismatch pii not_appropriate hate_speech sexual_content quality toxicity humor helpfulness creativity violence