That's not an unreasonable question, when you consider that most platforms (HN included, if I'm not mistaken) are pretty clear that the etiquette is that the downvote button isn't a "disagree" button.
Is the opposite also true? Is the upvote button not an "I agree" button? If it is, then the opposite is also true. Otherwise there really isn't a point to the vote buttons.
This part of the etiquette is obviously not uniformly respected. HN is still better at this than sites like reddit, but something tells me it's against human nature to upvote things we don't agree with - no matter how relevant they are.
> against human nature to upvote things we don't agree with
In this case you don't have to agree with the statement, only agree that it's unpopular. Maybe they're disagreeing with the facts in the statement's premise? Then they should say so, I think.