-4 is enough to shut down a conversation? What a terrible idea. How do we get rid of this mechanism?

I don't like it either, but Eliezer seems convinced that long conversations descending from posts by trolls (or, more often, sincere but badly mindkilled people) are destructive enough to site culture that they're worth going to great lengths to punish.

So, if you want the feature gone, he's the guy to talk to. Ideally in person.

-4 is enough to shut down a conversation? What a terrible idea.

In practice it doesn't happen all that often and there is a trivial workaround -- start a new (sub)thread quoting the downvoted post and indicate you want to continue talking...