Unfortunately the negative posters have more to gain. By putting down someone they get a minor lift up in their own self-image, while boosting someone does not

Unfortunately the negative posters have more to gain. By putting down someone they get a minor lift up in their own self-image, while boosting someone does not provide nearly such a strong reaction. I think it has more in common with the phenomenon where in general most feedback is negative because people who are happy with a product/situation tend to not bother looking for ways to express that opinion, where people with a strong negative opinion generally want to find a place they can vent.