Simply speaking, my gut tells me this isn't just about San Francisco. They don't have a monopoly on overexpensive housing, homelessness, drug problems, feces, violence, or taxes.
Again, anecdotal, but I think the exodus is real, and it's not hard to see why. We're going to soon hit a point where apologists for cities will no longer be able to defend them. I would love to live in a city if it didn't both punish success and fail to help those whom are truly in need.