This is a misunderstanding of how voting/promoting works. If someone is wrong you may want to promote them as much as someone who is right in the hopes of enlightening the masses.

Also, you may disagree with something and find it interesting still. In that case upvoting makes sense.

Upvoting != Agreeing. Unfortunately, when you do not have a button for agreeing or disagreeing, you are inclined to use the Vote button.