> And, morally, the place of original residence is responsible for them, not the taxpayers of San Francisco. If nothing else, people with longstanding ties to the community and economy should get preference for services

I believe you would find that this is illegal. Shapiro (Shapiro v. Thompson, 394 U.S. 618 (1969)) and its progeny address this issue on point.

(I feel obliged to mention I believe your number because of your expertise, simply because of the number of people in this thread who failed to say that).