I'm not totally sure, but I would say either upvote your favorite amongst the rebutting comments that will likely crop up if the incorrect post is highly rated,

I'm not totally sure, but I would say either upvote your favorite amongst the rebutting comments that will likely crop up if the incorrect post is highly rated, or stay quiet. Here's a different hypothetical where upvoting based on agreeing opinions, rather than quality of reasoning, can be a problem. It sometimes crops up in sites with rating systems like the one we are reading right now, and it could be on any blatantly wrong, or merely not-widely-held opinion. 1) A person writes "a comment that honestly and eloquently makes a claim based on the perceived fact that the world is flat" (or any other well-reasoned claim based on an incorrect premise, or simply an opinion which is disagreed with). 2) Either because it was well reasoned or because of a number of otherwise quiet flat earth believers agreeing with it, it gets up-voted highly. 3) A few passionate replies are written to rebut the highly voted claim, but the majority of which do so caustically, without good reasoning; perhaps even name-calling. 4) In order to push forth their opinion, people who believe the earth is round up-vote the rebuttals, regardless of their quality; and the tragedy is that sometimes (often?) the rebuttal most up-voted is one that simply appeared earliest, rather than the one which rebuts most clearly. So, I don't know what the ideal voting method would be, but voting based on quality of reasoning, not agreement, would have avoided this problem -- at least in the case of arguments. A side note: as others have noted, the distinction between "fact" and "opinion" is, well, a matter of opinion in many cases.