Downvote as feedback
It is simple and easy to upvote a UserVoice post, but the only way to give disagreeing constructive feedback is by having to click the comment link and to write a comment.
While the internet can be a place where the less pleasant side of people can surface under the guise of anonymity, it shouldn't diminish the positive potential constructive feedback even if it is not in agreement to the original post.
Not all suggestions and feedback is the same experience as others.
This is only meant to act as a indicator of the feeling within the community in both for and against.