His son was such an ásshole
I don't know how his son had such a terrible behaviour as well as being so rude towards his own father and others around him, plus those conversations he had about sex were just straight out weird.
I'm not gonna say that the suicide was the way to go, but he did make things easier for everyone, well, his father loved him no matter what (just like any out there who's a good father).
By the way, with a title like this I expected the film to be quite different than what I came across although I still liked it, and that grand ending showed how free Robin Williams felt as in that role and as a person.