Comments by banned users get killed by software. Community members who think the comment shouldn't be killed can always vouch for a dead comment (if they have karma > 30) by clicking on its timestamp to go to its page, then clicking 'vouch' at the top. If enough users do this, the comment is unkilled.
Killed comments are visible to anyone with 'showdead' set to 'yes' in their profile. We never delete comments outright except in the rare case where the author asks us to.
Killed comments are visible to anyone with 'showdead' set to 'yes' in their profile. We never delete comments outright except in the rare case where the author asks us to.