FJ being a forum relies on people using their words.  While the reputation system (and downvotes specifically) is meant to curtail some of the piling on that can happen when a bunch of members push back against another member's opinion, using it as some kind of "retaliation" is not the intended use.

If a member is posting while giving a bunch of downvotes or other negative  reactions that is fine.  A member who does nothing but downvote every post in a thread or chasing someone around the forum downvoting all their posts is using the system other than for its intended use and will no longer be allowed.

This rule does not mean you will be put on JTTH if you downvote or react negatively to posts.  This is for members (usually in problem threads) that have no other participation on the forum other than giving negative reputation reactions.