There is a moderation mechanism designed to do X when users do Y. If this mechanism is good, we should keep it. If this mechanism is bad, we should remove or modify it. But we should not think about this mechanism while voting. That's gaming the mechanism.

A mechanism requiring that it should not be thought about is a significant flaw. Stable systems rely on being robust with respect to people trying to achieve desired goals via them, at least to the degree that is practical. It so happens that I don't think the 'gaming' potential of this mechanism is actually especially significant. People downvoting a comments because "they want to see less of this entire thread" is not too much of a corruption away from "they want to see less of this". People do exactly this already, without this mechanism. In fact, they go through and systematically downvote every comment in a thread. Downvoting just the one is a net reduction in 'gaming', if that label applies at all.