“The dream of open borders captures the contempt with which progressives regard America’s sovereignty and the hard-won achievements of its people,” writes author David Horowitz in his book, “Big Agenda: President Trump’s Plan to Save America.”

The gist of this statement is right now playing out before our eyes on the southern border.

Thousands of Central American migrants, mostly Hondurans, have joined caravans in recent weeks in an aim to request asylum in the United States.

Embedded among them, near the U.S. border in Tijuana, is caravan organizer Luis Cruz, who is with the immigrant rights group Pueblo Sin Fronteras.

On Sunday, Cruz delivered an audacious message to President Donald Trump and the Trump administration.

“Let these people in. Let them try. Let them try,” Cruz told Fox News’ Griff Jenkins. “I mean, most of these people are not bad,” he said.

For legions of migrants, it’s not their character that’s being questioned but their willingness to flagrantly flout U.S. immigration law.

As for the concerns that criminals could be traveling with the caravan, Cruz actually told Jenkins that there’s no way to identify and separate the potential criminals.

“We don’t know if they’re part of a gang, if they’re gang members or not, because they hide,” Cruz said.

Not so.

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A convicted murderer from Honduras was arrested after illegally entering the U.S. with members of the migrant caravan, officials with the Department of Homeland Security said on Friday.

“As DHS confirmed weeks ago, there are at least 600 known criminals in the caravan flow,” said Tyler Houlton, a department spokesman. “The fact that Border Patrol arrested a murderer within the first caravan-related apprehensions at our southern border proves how real the threat of the caravan is to our national security and public safety.”

“Not being a bad person is not the threshold criterion for admission to the United States,” Ira Mehlman, media director of the D.C.-based Federation for American Immigration Reform (FAIR), told LifeZette on Monday. “There are some 7.4 billion people on the planet Earth who are not U.S. citizens. The vast majority of them are not bad people, but it is absurd to suggest that we should let them all in and ‘let them try.’”

“The migrants in the caravan are almost all economic migrants fleeing poor economic conditions in their homelands, not people who are fleeing political persecution,” he added. “Billions of people around the world are as poor, or poorer, than those in the caravan. It is simply unfeasible to accommodate everyone who would be economically better off by coming to this country.”

“The United States has an additional responsibility to make sure that people who pose a danger to the country are not permitted to enter,” said Mehlman.

Cruz’s message to President Trump came on the same day Mexican authorities shut down a crowded shelter at a sports complex in Tijuana, citing “bad sanitary conditions,” according to a number of outlets.

Caravan migrants are suffering from respiratory infections, tuberculosis, chickenpox and other serious health issues, Tijuana’s Health Department warned recently.

Nearly 2,300 people — or more than a third of them — are being treated for health-related issues, including HIV/AIDs, according to Fox News and other sources.

There’s also concern about a hepatitis outbreak.

Meanwhile, hundreds of migrants from Central America in Tijuana are planning to return home.

In an interesting turn of events, they are blaming Pueblos Sin Fronteras — Cruz’s group — for allegedly misleading them into joining the caravan with false promises of easy asylum in the US.

“Pueblos Sin Fronteras told us not to worry, that there was going to be transportation, that Mexico was going to open the gates so that we didn’t have to enter [the U.S.] illegally, via the river,” Ulises López, who came from Honduras, said in a Mexico Daily News article.

Several thousand Central American were offered benefits in Mexico if they applied for refugee status and stayed in the country’s two southernmost states.

“What was offered to the caravan of Honduran migrants was a trap,” Lopez said, adding that Pueblo Sin Fronteras “took advantage of us, they used us in a horrific way, what they did to us has no name.”

Also noteworthy: Several thousand Central American were offered benefits in Mexico if they applied for refugee status and stayed in the country’s two southernmost states.

Instead, they decided to keep their eyes on the prize: asylum in America.

For some, that plan is backfiring.

Elizabeth Economou is a former CNBC staff writer and adjunct professor. Follow her on Twitter