What you're describing isn't clear. I assume you meant to say "If someone comments on your negative comment ..." otherwise it appears you're describing how upvotes are generally expected to work.

I expect HNs algos could spot such a comment thread quite easily (thereby avoiding what you've described). That doesn't require a new user feature.

That could be solved by "if user has downvoted the comment they reply to, don't count upvotes for their reply when calculating thread value".