Victor Davis Hanson warns at National Review Online that an unwillingness to follow the law leads to serious negative consequences.

What makes citizens obey the law is not always their sterling character. Instead, fear of punishment — the shame of arrest, fines, or imprisonment — more often makes us comply with laws. Law enforcement is not just a way to deal with individual violators but also a way to remind society at large that there can be no civilization without legality.

Or, as 17th-century British statesman George Savile famously put it: “Men are not hanged for stealing horses, but that horses may not be stolen.”

In the modern world, we call such prompt, uniform, and guaranteed law enforcement “deterrence,” from the Latin verb meaning “to frighten away.” One protester who disrupts a speech is not the problem. But if unpunished, he green-lights hundreds more like him.

Worse still, when one law is left unenforced, then all sorts of other laws are weakened.

The result of hundreds of “sanctuary cities” is not just to forbid full immigration enforcement in particular jurisdictions. They also signal that U.S. immigration law, and by extension other laws, can be ignored.

The presence of an estimated 12 million or more foreign nationals unlawfully living in the U.S. without legal consequence sends a similar message. The logical result is the current caravan of thousands of Central Americans now inching its way northward to enter the U.S. illegally.

If the border were secure, immigration laws enforced, and illegal residence phased out, deterrence would be reestablished and there would likely be no caravan.