As far as I can tell, all three replies to that comment were made before it hit -3.

(I know that my reply was made with no penalty, and Yvain's reply was already there at the time; wedrifid's later comment also suggests that his reply wasn't penalized.)

You know what would have prevented this?

If you'd told me in June, when I asked you for moderation guidelines beyond "kill shoe ads", that I should ban comments like that.

(paid a karma cost to respond to this comment)

Perhaps it should just be impossible to reply to anything if there's more than two ancestors at -3 or below.

But then, the circumvention will be to stop using threaded comments properly and start new comment threads to reply to comments below the threshold.