For example, if a person has had a bad experience being harassed by a coworker and writes a clear and honest comment about this as a problem, that can be easily interpreted (such as by a person unfamiliar with getting harassed) as an uncivil thing to say about your coworker. There is a known pattern of "tone policing" - that people have a pattern of asking less-privileged people to be "not so angry-sounding" when talking about something problematic or upsetting from their lives. I think of this pattern as a defense mechanism to protect yourself from understanding somebody else's pain (especially if it challenges something about your status), and it seems likely to be a bias here, even an unconscious bias.
Instead, I'd love to see explicit standards for comments on a visible community guidelines page, and an efficient flagging system that reinforces these guidelines.