Every time you see a comment marked as [dead] that means a moderator deleted it. There is no auto-deletion resulting from downvotes.
Even mentioning certain topics, such as Israel's invasion of Palestine, even when the mention is on-topic and not disruptive, as in this comment you are reading, is practically a death sentence for a comment. Not because of votes, but because of the moderators. Downvotes may prioritize which comments go in front of moderators (we don't know) but moderators make the final decision; comments that are downvoted but not removed merely stick around in a light grey colour.
By enabling showdead in your user preferences and using the site for a while, especially reading controversial threads, you can get a feel for what kinds of comments are deleted by moderators exercising. It is clear that most moderation is about editorial control and not simply the removal of disruption.
This comment may be dead by the time you read it, due to the
previous mention of Palestine - hi to users with showdead enabled. Its parent will probably merely be down voted because it's wrong but doesn't contain anything that would irk the mods.
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.
Even mentioning certain topics, such as Israel's invasion of Palestine, even when the mention is on-topic and not disruptive, as in this comment you are reading, is practically a death sentence for a comment. Not because of votes, but because of the moderators. Downvotes may prioritize which comments go in front of moderators (we don't know) but moderators make the final decision; comments that are downvoted but not removed merely stick around in a light grey colour.
By enabling showdead in your user preferences and using the site for a while, especially reading controversial threads, you can get a feel for what kinds of comments are deleted by moderators exercising. It is clear that most moderation is about editorial control and not simply the removal of disruption.
This comment may be dead by the time you read it, due to the previous mention of Palestine - hi to users with showdead enabled. Its parent will probably merely be down voted because it's wrong but doesn't contain anything that would irk the mods.