Though Charly undergoes a remarkable I.Q. increase, his gentle nature remains the same, whether he is functionally retarded or a genius. Unscrupulous people take advantage of his gentle nature, like his two "friends" Joe and Frank.
However, Charly becomes more and more aware of the ulterior motives of some people in Part II. Witnessing a mentally challenged man get humiliated, Charley's anger and empathy are inflamed. He shouts:
Suddenly, I was furious at myself and all those who were smirking at him I wanted to pick up the dishes and throw them. I wanted to smash their laughing faces. I jumped up and shouted. "Shut up! Leave him alone! He can't understand. He can't help what he is...but for God's sake, have some respect! He's a human being!"
The "vulnerable groups in society today" are the same ones Keyes was writing about in 1958. Those who are "different" are always at risk of misunderstanding, mistreatment, and even abuse.