I think the title is a bit misplaced. The point is not that positive thinking is bad, but that you will likely be happier focusing on your relationship with others and accepting yourself as you are, as opposed to trying to make yourself "better". The title is linkbait that only vaguely references the material in the article.

Still, I thought the article pretty good. A key insight was a quote by Dr. Neel Burton:

"In traditional cultures, people lived in very close knit communities. They knew each other, and they didn’t really focus on themselves so much. The focus on life was on the survival community and not on their own individuality. Modern society is very different from that. There’s a huge emphasis on me; my goals, my life, my death. That puts a lot of pressure on people, and it’s not the kind of pressure that we’re evolved to cope with. That’s the source of many of our problems."