Comments that are marked [dead] without the [flagged] indicator are like that because the user that posted the comment has been banned. For green (new) accounts

Comments that are marked [dead] without the [flagged] indicator are like that because the user that posted the comment has been banned. For green (new) accounts this can be due to automatic filters that threw up false positives for new accounts. For old accounts this shows that the account (not the individual comment) has been banned by moderators. Users who have been banned can email hn@ycombinator.com pledging to follow the rules in the future and they'll be granted another chance. Even if a user remains banned, you can unhide a good [dead] comment by clicking on its timestamp and clicking "vouch." Comments are marked [flagged] [dead] when ordinary users have clicked on the timestamp and selected "flag." So user downvotes cannot kill a comment, but flagging by ordinary non-moderator users can kill it.