What is Abnormal? Fear, Phobia, and Stigma

I think the stigma attached to having a psychological illness is not as strong as in the past because a psychological illness is got more recognition as illness by public. However, I think that the discrimination for people who are having a psychological illness still remains deeply in my society.
I have been thinking why Peter said the novel we are reading supports this topic. There are no related between this topic and the novel because the main character, Lennie, looks like handicapped. I know this word is including of the expression of discrimination. I look up the word, which is handicapped, after that I found that it is one of the illnesses. It connects “abnormality” which a problem which is “serious enough to disrupt everyday life.”