The thing is, downvoting directly makes a comment less visible. The point is more any managing SNR than the feelings of the poster, so downvoting is still the right thing even if you're worried about rewarding them with negative attention. But even then, they know a downvote means several more people won't see their comment at all. And most people genuinely still don't like downvotes, so they're an effective signal of what's accepted or not in the community. In short, the poster's feelings are pretty irrelevant when it comes to downvoting.