Indeed. I agree with Kanewolf. They never gave this option, just to avoid this feature from being misused. People actually abuse such kind of features, as far as I can tell from my experience. Also, giving a dislike can also start harsh arguments, or even a flame war to some extent. Depends on the type of forum as well though.
Though, we can Up-vote or Down-vote any comment or reply/answer, which is actually acceptable and is different as well, but like mentioned above, if there are any fishy posts, then just report/flag that comment.
Even for the up/down vote option, we need to carefully and wisely choose whether the solution given is indeed wrong or correct. Can't misuse it either.