>Negative comments tend to accurately reflect the human condition and challenges that people face, where positive comments tend to be "put on a happy face and pretend everything is fine", which is harder to identify with.

That all depends on your mental state. If you are in a happy place, positive posts will be easy to identify with. If you are in an unhappy place, negative posts will be easier to identify with.

The kicker is, a negative post can more easily shift people from happy to unhappy then a positive post can shift people from unhappy to happy. This is true outside of social media as well. People are more willing to believe negative things said about themselves over positive things. We are out own worst critics.