Flagging is one thing, but I assume that there is a human in the loop before a user is put in the dead state.

There isn't. Almost everything you see that's killed has been put into that state without any moderator action. We review the ones we have time to review but that can be hours or days later, and we don't get to them all because there are so many (though users can vouch them or email us to bring anything to our attention to be reviewed).

Further, even if we leave something dead, it's no indication of any "agreement" or "endorsement" of anything. We're not here to promote any editorial line. All we care about is whether a comment is within the guidelines:

https://news.ycombinator.com/newsguidelines.html

How much karma do you need to have before you're trusted to flag and vouch for comments?

A trivial amount you've had for ages (31 karma[0] - although it's not public, I'm sure the unofficial guides adjust accordingly)

[0]: https://github.com/minimaxir/hacker-news-undocumented#flaggi...

I wonder why I've never had that ability then.

You have to click on the time of a comment (eg "2 days ago", "1 hour ago") to see the [flag] link, and you have to have show-dead turned on to see the [vouch] links. They're not super obvious in the UI by default, but you probably have the ability. You'll see a lot more bots/spammers/noise if you have show-dead turned on.

Wow thanks. I’ve probably spent a thousand hours reading hacker news comments and never noticed.