I have struggled with similar issues my whole life. It is right to empathize with his depression, but it is just as disrespectful (in my opinion) to prescribe any thoughts to his suicide. Everyone experiences different aspects of depression and he was no different. In his world, the lack of opportunity or interest may have literally killed him.
I think it says much more about you to say that this judgement is unnecessarily harsh. Franzen undoubtedly loved his friend, even if they had a strange relationship through their passion for writing and Americans. I truly believe that this is, at least in part, Franzen's effort to pay respects to his friend.