Well I am quite certain I have no idea what I was talking about in that original review. In that I seemed to miss the entire intention of Arkin's performance the first time I watched the film. Although the film is on the surface the "different" man helping the "normal" people that is not the simple truth to Arkin's portrayal of John Singer. From the outset of the film he establishes a palatable loneliness that defines his performance, something I somehow did not pick up on the first time around. This is what Arkin uses though to effectively define his character as we see in his earliest scene where he interacts with his fellow mute Spiros. Arkin provides the direct joy just in the act of the interaction but without that moments of interaction Arkin shows that Singer recedes into a certain depression. A voiceless depression of course that Arkin effectively internalizes in his work as such an essential though unfortunate part of the man as well as Arkin's performance. Arkin creates that need necessary to make it convincing that Singer moves a great distance to be closer to Spiros, after he is committed due to his erratic behavior, and Singer begins a new life in that town.
Arkin's establishment of Singer's motivations is pivotal in that he shows that he's neither some otherworldly helper nor is some strange user of people. Arkin finds the right method within his portrayal of Singer's manner when he interacts with the various people he comes across. Singer is always trying to help just about any one who needs it. Arkin doesn't depict this at a saintly distance, even with the lack of speaking, nor does he portray it as any sort of unnatural need from Singer. Instead Arkin depicts the very humble yet deeply humane behavior as Singer's ways of just trying to connect with other people, and share life with them. The is a simple appreciation that Arkin reveals in Singer of just any moment of communication as he reveals Singer being able to enjoy that connection for a moment. When he is not doing so Arkin reveals the man stuck in his unfortunate literal silence, and Arkin offers such poignancy by infusing into Singer's behavior such a honest desire for a bit of human companionship. Arkin never allows himself to be a caricature, or overly saccharine through creating that intense need while never making it off putting either.
Throughout the film Singer does his best to try to help others sometimes he succeeds sometimes he does not. There is something interesting in this though in that Arkin is simultaneous heartwarming and heartbreaking in every single one of his causes. The reason being Arkin does depict that most generous of attitudes with such genuine earnestness as well as so honestly realizes that bit happiness when the people pay him mind. The problem is though even as he helps them the others are often so caught up in their own problems that they still pay little attention to Singer, even when he has helped them. A few of Arkin's reactions are absolutely devastating because he does not depict any hatred or anger as they ignore him, but just that quiet return to somberness as they leave him out of their lives once again. The only guarantee for companionship is with Spiros, but even this Arkin sadly reveals also as still often one sided. What Arkin does throughout his performance, and again I don't know how I did not see it the first time, is set up Singer's downfall by making his sorrow from his loneliness a constant. He shows it being alleviated at times, but never gone. When he loses Spiros, Arkin reveals the man left without even his final safety net expressing the full extent of anguish in his eyes as he looks over his only friend's grave while leaving his final act a terrible inevitability.