Advocates claim that “sanctuary,” as they call it, achieves a moral goal — peace of mind for people who, whatever their immigration status, are often longtime residents, leading productive lives — at little or no practical risk or cost to anyone.

This all-upside argument was explicitly incorporated into the “Due Process for All” ordinance that San Francisco adopted on Sept. 24, 2013. The law was a reaction to “Secure Communities,” the program under which the Obama administration sent so-called “detainer” requests to local officials to hold illegal immigrants 48 hours beyond their otherwise lawful jail time, so the feds could come deport them…

Alas, like many win-win scenarios, the one propounded by West Coast sanctuary advocates was a bit too good to be true. This should have been obvious even before the seemingly random alleged murder of Kathryn Steinle by an illegal immigrant, Juan Francisco Lopez-Sanchez, whom the San Francisco authorities had recently released from jail pursuant to the Due Process for All ordinance, despite an urgent request from the Department of Homeland Security that he be held for deportation — it would have been his sixth — to Mexico.

If proponents of sanctuary had been more candid, they would have acknowledged that their policy carried risks as well as benefits. It inevitably raised the chance some dangerous individual would wind up back on the streets, and that, however remote the probability of such an event might be, it could be catastrophic to the unlucky victim.