I personally have posted mathematically provable facts that happened to go against popular opinion be downvoted into negativity, so I wouldn't say it's that rare.
On the whole, the general behavior seems to trend towards upvoting interestingness, but it's by no means insanely uncommon at all, I think.
It's rare for a well articulated, reasonable, relevant, respectful opinion to be downvoted. But recall, a statement can be mathematically provable and yet fail on another of those points.
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Since you brought it up: in the specific case you're probably referring to [0], you say that you're "not sure exactly what [the parent post is] taking issue with", but the original author of the piece responded to the parent post letting him know he'd corrected his mistake [1]. So while your assertion was technically mathematically correct, I would say it was not relevant, and in fact was dismissive of a relevant concern, which I think explains the downvotes. I do not think it's fair to characterize it as being downvoted because it "happened to go against popular opinion". (I cannot say for sure; I did not vote on any of those comments, but I think I understand the sentiment of those who did.)
I'm glad you brought it up -- I figured it was bad form to do so personally, and was even ashamed of posting the comment you responded to here.
That said, I didn't see Max Klein's response, so I'm quite glad you pointed that out to me, as it was curious; However, I don't feel I was dismissive in the slightest. In light of the correction, I can see how others could view my stance as at odds with reality, but I personally didn't see cause for concern. Again though, my reading / interpretation of the statement was clearly not what was intended, so my logic is predicated upon a fallacy.
I feel I understand it much better now that you've brought it up, because I was honestly dumbfounded at the time.
Still, so as not to betray my Irish stubbornness, it _was_ mathematically correct. ;-)
On the whole, the general behavior seems to trend towards upvoting interestingness, but it's by no means insanely uncommon at all, I think.