Do social norms cause mental illness?

On the question about fatness, the discussion came around to an article that said that we have a natural body weight, and we can’t get away from it unless we have a starvation diet that would be diagnosed as anorexia in a thin person. There was at least one example of this provided by a jelly.

It made me wonder if this is a pattern. Is mental illness caused when we have social norms that some people can not conform to? Could society be more tolerant, and if they were, would a lot of mental illness disappear, just as if we were more tolerant of people being overweight, the social pressure to be thin might disappear? If we did this, would we be able to get rid of a lot of mental illness, simply because more people would feel like they belonged?