In some instances of mental illness suicide may be a choice. When my son was battling severe depression he often wrote about his feelings. It appeared at times that he would have chosen death if given the opportunity as he wrote here, "Demand for the cure. A cure for such an incredible amount of suffering, that has brought me nothing but agony. Death is my choice to rid me of my penalty."
No one knows what it is like to be on the precipice of suicide and then to kill yourself, no one can tell you how they felt or whether they had a choice, because they are no longer here. To say "Robin Williams didn't die from a disease, he died from his choice" is saying that you know what he felt and what he was thinking. It is to say that the disease wasn't relevant enough to have killed him inside already, before his body was killed. It is to say that you are a mind reader. It is to say that you are a god, and we know that is not true.
Is there hope out there for those who struggle with severe, debilitating depression? Absolutely! There will always be hope, but maybe not control or dare I say it? Choice.