It's no surprise that Mayor Gavin Newsom wants to put a sit/lie law on the ballot, and it has absolutely nothing to do with the fact that the supervisors are moving slowly on his proposal. It has nothing to do with any facts -- the cops could enforce existing laws and address the problem.
No, this is all about politics. Newsom never wanted the supervisors to approve a sit.lie law; he and his operatives want to put it on the November ballot, so they can use it as a wedge issue to attack progressive candidates. They can also use it to raise money, which can be spread around through slate cards to support his supervisorial picks.
Remember, this is how Newsom got elected mayor: He picked a wedge issue (general assistance payments to homeless people), created a slogan ("care, not cash"), raised a ton of money, and made it his signature campaign strategy. It worked, so he's trying again.
Before Arthur Evans leaps in and attacks me, let me say: I know there are people in the Haight who want this law. (There are also people in the Haight, including the venerable Haight Ashbury Neighborhood Council, who oppose it.) But I don't think Newsom really cares about that; if he did, he'd work with the supervisors on a compromise or alternatives. Instead, he's refusing to participate in the board's debates.
This is all about November's board elections. Sorry, Arthur, but your pet cause is now the mayor's political tool.