Jim Steinle, second from left, father of Kathryn Steinle, in photograph, testifies before a Senate Judiciary hearing on the Administration's immigration enforcement policies. (Molly Riley/AP)
Opinion writer

In reality, there is no free lunch. In the alternate reality known as the American political debate, however, that’s the only kind on the menu.

Conservatives say tax cuts boost economic growth, which yields higher revenue. No need to worry about bigger budget deficits.

Meanwhile, over on the left, we have laws and policies in more than 200 jurisdictions, including some of the largest cities and counties in the country, that are meant to protect immigrant communities by preventing local authorities from cooperating with federal deportations of undocumented immigrants who have run-ins with the law.

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.

Sanctuary laws are in the national spotlight after an illegal immigrant with prior deportations and a criminal history pleaded not guilty to murdering a woman at a San Francisco pier. Here is what you need to know about those laws and how they protect illegal immigrants. (Jayne W. Orenstein and Osman Malik/The Washington Post)

The ordinance states that “a law enforcement official shall not detain an individual on the basis of a civil immigration detainer after that individual becomes eligible for release from custody” unless that person was currently charged with a violent felony and had been convicted of another within the past seven years.

Its preamble claimed that Secure Communities, by associating the police with immigration authorities, “undermine[d] community trust of law enforcement by instilling fear in immigrant communities of coming forward to report crimes and cooperate with local law enforcement.” What’s more, the preamble noted, holding people pending deportation costs money that could be spent on more pressing law-enforcement needs. In other words, sanctuary actually improves public safety. The legislation duly cited social-science reports in support of these contentions.

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.

Political activists don’t do nuance, though — especially not when discussing immigration. In that polarized debate, everyone has to be either a sainted Dreamer or, to hear Donald Trump tell it, Mexican riff-raff.

To be sure, sanctuary proponents played down the potential risks in part because they don’t want to give the likes of Trump even that much credence. This is understandable, given both political realities and the fact that the vast majority of illegal immigrants in this country are, indeed, here to work and better their lot, not to commit crime.

Indeed, the surge in illegal immigration from Mexico that began in the 1990s (and has now leveled off) coincided with a dramatic decline in the U.S. crime rate, which is not what you would expect if Mexico were purposely sending its undesirables across the border, as Trump suggested.

Still, in hindsight, the sanctuary movement’s judgment, political and moral, doesn’t look too wise. San Francisco took an extreme position — it refused assistance to the Obama administration even after the administration abandoned Secure Communities last year and replaced it with guidelines much more carefully focused on serious criminal offenders.

Consequently, a woman is dead — and there’s a huge political backlash, with Congress threatening to withhold federal funding from cities, such as San Francisco, that refuse cooperation with federal immigration authorities.

Even if those bills don’t pass, and they probably won’t, the broader cause that the sanctuary movement was meant to advance has been set back, perhaps permanently. Just about no one is rushing to San Francisco’s defense.

There’s a lesson here, and it applies beyond this particular case: In the long run, intellectual honesty is the best policy.

Read more from Charles Lane’s archive, follow him on Twitter or subscribe to his updates on Facebook.