> and it's common to see perfectly reasonable satements of fact (much less opinions) that someone else doesn't like be downvoted.

I don't see why "reasonable statements of fact" being downvoted to be a problem. Something can be a reasonable statement of fact without contributing substantially the discussion. That's a perfectly good reason to dislike it being presented in the context, and a perfectly good reason to downvote it.

pg may have said it is acceptable to use downvotes for disagreement, but that doesn't mean that downvote implies disagreement. Being a fact doesn't, on its own, make something a productive addition to the discussion.