This hypothetical "factually wrong" dilemma is a red herring. The real issue is disagreement, not factual correction. Much more often the case is that someone has written a thoughtful, honest comment based on some worldview that is very different from your own. In that scenario you should not downvote at all. Rather, take the time to explain your own worldview or just move on.

The "factually wrong dilemma" is in no way a red herring. It's actually precisely the point I was responding to in the grandparent post. Down-voting based on opinion is something else entirely. Of course, people will confuse opinion and fact sometimes, and I would encourage people to be skeptical of themselves on delineating the two, but that doesn't invalidate the idea that people can say things that are factually wrong.

Yes, if someone says something that is factually correct (or at least not incorrect) based on a different world-view, then I agree, don't vote them down. If they say something that is factually incorrect but accepted in their worldview, I don't know that that changes what I was saying before.

Edit: you know, it's usually my policy not to comment on how comments have been modded, but I do find it hilarious that in this discussion, someone's down-voted this comment (at the time of this edit) without replying.

To the sibling comment: yes, I agree on the main point and am just discussing a finer point, an issue that was raised by an earlier comment on this chain.

Voting based on opinion reinforces groupthink. Voting based on fact helps keep the level of discussion high.

It's a red herring because the problem that the OP is trying to get at is not about factually incorrect comments. The important message is that you shouldn't downvote comments you disagree with, and instead we're nitpicking about how to be the fact police.

Maybe it's because we already agree on the main point, and are just trying to settle the finer points?

What I would do personally:

  if score < 1
    option 1
  else
    option 3

But of course it's a judgment call. If it seems like the person is intentionally trolling, then by all means, go negative. If the person is just misinformed, zero is a sufficient slap on the wrist that hopefully says "make sure you know what you are talking about next time", and a reply makes it obvious why it got downvoted.

For me, it's:

  if score < 2
    option 1
  else
    option 3

Note that I don't want to penalize them for being wrong-- we've all been there (and sometimes when we think they're wrong, really we are). It's better to let them lie and reply with better information or a ("Are you sure that's right? I recall blahblah.")

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.

A comment like that requires a reply. If you don't have the time, that's okay b/c someone probably will (but you could check back later to make sure someone has).

Don't punish (downvote) someone for earnestly taking part in the conversation. Other people probably have similar beliefs so this person did everyone a service by bringing the question out into the open so it can be discussed.

Votes encourage discussion, not correctness.

"...eloquently makes a claim based on the perceived fact that the world is flat."

You should do what feels right to you.

What would I do? Probably click reply and challenge my fellow hackers with something like, "Who you gonna listen to, Galileo or Thomas Friedman?"

I agree that one should do what feels right.

FWIW, I was trying to posit a situation in which you don't have time to respond. I was using flat earth as a stand-in for a wrong statement, and oftentimes, it takes more than name-dropping Galileo to demonstrate that the writer is factually incorrect. I agree that if you have time, demonstrating the truth is the best option.