I see it a lot. What's worse is up and down votes are a corrective mechanism.

If you get downvoted, that kinda feels bad, if you get upvoted, that kinda feels good. It shapes your discussion and teaches you the rules of what the community finds acceptable/unacceptable.

What is the honest to god pragmatic result of this policy?

You're training people not to say something others disagree with.

Even if you don't agree with that, downvote to disagree causes pragmatic problems outside of training! Consider a discussion where someone starts off with an unpopular view, and then an interesting discussion happens back and forth between two parties discussing that position. Downvote to disagree hides that discussion.