I saw that HBO documentary about John Cazale and it was very good. You don't realize how many great movies he appeared in until they list all the flicks and how many Oscars they won.
I think its normal & healthy human nature to sympathize/empathize with anyone that appears to be weak or fragile. To not, in my opinion, is dysfunctional and a key characteristic of a sociopath and quite frankly a person who tends to be a bully. Also, I think everybody knows a "Fredo" in their life... how do you treat them?

(By the way - when we played "Godfather" in the neighborhood back in the day, NOBODY wanted to be Fredo!)