Do you ever find yourself in a scary situation where you start spontaneously reciting the 23rd Psalm? You know, “The Lord is my shepherd … “?

Well, a new movie, “Trade,” gave me the shuddering feeling that I needed protection from wickedness – that we all do, that America does.

“Trade,” starring Kevin Kline, opening Friday, is a fictionalized look – sometimes lurid, always harrowing and, by the end, profoundly spiritual – at the sex-trafficking industry, demonstrating clear and present danger to our national well-being.

The genesis of “Trade” was a 9,000-word article by Peter Landesman appearing in The New York Times Magazine on Jan. 25, 2004. Landesman chronicled the international sex-trafficking business, stretching from Eastern Europe to Mexico to such ordinary places as Plainfield, N.J., where in 2002 police raided a house and rescued four Mexican girls, ages 14 to 17, working as sex slaves.

That’s sex slaves, not prostitutes.

Landesman described an interior that was the “land-based equivalent of a 19th-century slave ship, with rancid, doorless bathrooms, bare, putrid mattresses; and a stash of penicillin, ‘morning after’ pills and misoprostol, an anti-ulcer medication that can induce abortion.”

This was here in America.

Landesman cited government estimates suggesting that there could be as many as 50,000 such sex slaves in the United States, although nobody really knows; as a State Department official told him, “We’re not finding victims in the United States because we’re not looking for them.”

The reaction to Landesman’s article has been revealing. Left-libertarians, who take their political cues from the American Civil Liberties Union, savaged the article. Jack Shafer, writing the “Press Box” column for Slate.com at the time, launched a fusillade against Landesman’s truthfulness.

Last Sunday, The Washington Post presented a front-page article finding that only 1,362 such cases have been identified by authorities since 2000. This story inspired Shafer to follow up with yet another piece attacking Landesman and “Trade,” headlined, “The Sex-Slavery Epidemic That Wasn’t.”

If one were conspiratorial, one would say there’s been an organized campaign to minimize the sex-trafficking problem on the eve of the movie’s release.

Some might say that 1,362 is a big number when human beings are involved. The fate of the “Jena 6” – the six black Louisiana teenagers involved in a racially tinged brawl – has provoked a national outcry. That’s the way we are, or should be; we should care about each other, and we should worry about injustice, wherever it is found, in whatever quantity.

In a recent interview, Landesman defended his credibility, as well as the plot line of “Trade.” While the story is fictional, all the “mechanics of sex trafficking” depicted in the movie – the kidnapping in Mexico, the transporting across the border, the online auctioning of girls for sexual exploitation – are “100 percent true.”

As for the number of only 1,362?

“For every case they know about, there have to be hundreds they don’t,” Landesman answered. “How many kilos of imported cocaine do the feds actually see?”

For my part, I will say this: If the number of sex-trafficked girls – and boys – is greater than zero, we have a problem. Specifically, we are suffering from a criminal and moral cancer that will force us to take an even harder look at border security, and perhaps also the use of the Internet for nefarious purposes.

Alas, “Trade” is likely to get trashed for political reasons. Already, Variety has slammed it, worrying that the film will “further the psychic and political divide between the U.S. and Mexico.”

Even as the critics rage, “Trade” is worth seeing. But it wouldn’t hurt to remember the sacred words: “Yea, though I walk through the valley of the shadow of death, I will fear no evil.”

Because you will need some moral or psychic armor. And then steely resolve to fix this shameful problem.