I thought part of the point of the -5 penalty was to keep interesting discussions from happening down stream of downvoted comments. In that case isn't responding to heavily downvoted comments in a different thread exactly what should happen?

I assumed that either Eliezer just didn't like the subject or that the comment actually quoted a -5 comment. Hang on. This can be checked. We can see from Eliezer's page which author Eliezer was replying to and look at that user's page.

(From what I can tell everything the user in question has written has been downvoted.)