When you're stupid, you don't know it and life is so easy. Have you ever seen a depressed mentally handicapped person? I envy that.
Are you saying that mentally handicapped people can't suffer from depression?
That's what I've observed.
Living with a mental handicap is very difficult. It's wrong to think that all mentally handicapped people are happy because many are probably not happy, we can't be certain. Try to put yourself in their shoes and imagine what their life is like.