I find this post completely ignorant. For starters, mental illness is a holistic issue as much as it is a chemical/medical issue. Anyone with a mental illness who has taken ownership of its symptoms through all the channels available to them to circumvent any detriment it has on their life; including family, social, and career; can be a good developer, father, friend, mentor to other developers, team lead, CTO, etc... if that is their chosen path. You obviously have only experienced people with mental illness who are not being treated or treating themselves properly. I bet you have also had great experiences with developers with mental illness because you had no fucking clue they were suffering from it, because they were using the tools available too them to have a great quality of life and enjoy their careers as aspiring, hungry, productive and bleeding edge coders.
and I think the title of your post should be, "I am not fit to be on a team with mentally ill developers!"