I think many writers write because it's a convenient way to explain themselves to themselves. We take the chaos and the turmoil and the bullshit of our lives, and we make it into something that has a harmonious shape and sound.
When I started writing Tales of the City I was one year away from being a mental illness. It wasn't until 1975 that the American Psychiatric Association took homosexuality off the list of mental illnesses - and in many states, including the state of North Carolina where I grew up, homosexuality was a crime. An arrestable crime. It still is, in many parts of the world.
Writing is too hard not to do exactly what you want to do. It's a very draining and agonizing process for me, and I don't want to live with any piece of work that I don't believe in completely. I have to believe completely in what I'm doing. It has grown organically out of my own experience.