The psychological need for security is important.  The people who formulate our politic know that can can often use our natural tendencies to gain our acceptance of polices that make little sense, from a strictly rational point of view.  Border walls and the many issues that surround them occupy this idealized territory as the amount of actual security provided is quite limited, but the psychological return on investment is huge. Eric Schewe writing at The JSTOR daily site looks into this feature of the walls we build, ostensibly to protect ourselves:

 

In this column, I’ve explored the idea that security ideology creates a mirror version of the world around us. Beyond any specific technology or procedure, security “works” when it makes us believe that it solves an identified problem. This is not to deny the real risks of death or injury as a result of terrorism—but only to point out that satisfying beliefs is security’s highest priority. This is why we have spent billions of dollars and uncountable hours on security theater although terrorists have killed only sixty-five Americans per year since 2002. Terrorism receives a disproportionate amount of news coverage compared to say, car accidents, which kill tens of thousands of Americans every year.

The American political system is now seized by conflict over the symbolic threat of illegal immigration. President Trump has proposed an equally symbolic solution—building a bigger border wall. Interestingly, while vilifying illegal immigrants to his supporters as violent criminals, he has not penalized the industries that rely on their labor. After settling the budget standoff that shuttered the federal government for a month, he declared a national emergency to fund wall construction, although he immediately admitted there was no emergency—that he “didn’t need to do this.”

[..]

Every border wall has a particular historical context behind its creation. Yet they all announce the same message to the world: Our diplomatic and economic relationships with our neighbors have failed, and we are unwilling to repair them.

I’m in agreement with Eric’s conclusion.  Wall are indeed a testament to our failures.