If it's a seriously misguided but good-faith comment by a newbie, I might want to downvote it and explain why I did it. Hanlon's razor.
But, if it's a newbie and you knew that changing it from a -3 to a -4 would end the discussion, wouldn't you just not down vote it, and explain your problem or correction?
This new change seems to me to be a way for someone to end a conversation, though they had to have 3 other people help them get it there. Is that an intentional change we want to make?
I just found out that a new website feature was implemented 2 days ago. If a comment is voted to -4 or below, it and all replies and downstream comments from it will be hidden from Recent Comments, and further replies in that subthread will incur 5 karma points penalty. The hiding, but not karma penalty, applies retroactively to comments in that subthread posted before the -4 vote.
This seems to be worth a discussion post since most people are probably still voting things to below -3 without knowing the new consequences of doing so.