No negative button
I think that like Facebook, there should be no down vote button on discussions because it may upset people. If you don't like their ideas, then do not do anything. It may demotivate them especially people who comment in the language they are learning and are making mistakes and are not confident. A lot of discussions on here are voted really badly and it is a bit unfair to do that.
Usually, when a post has lots of negatives, it is a sign to moderators that this is either spam, or a disrespectful post. It usually proves useful, but, there is no doubt that one can feel bad when they make a completely relevant post that no one wants to hear about. Check out the "Google is awesome" post for instance.
I think it is more useful than good, and I think a lot of people could back me up on that. Especially the moderators. It makes their job so much easier. And, if someone gets downvoted for something perfectly relevant, then why should they care? It's the jerk who downvoted them for no reason who should feel ashamed.