Even the most stubborn retard knows it's not difficult to see drones are cheaper than a physical wall. You still have to monitor the space somehow, whether it's to see if someone is scaling the wall or digging a tunnel under it or whatever. So either you send patrols around in trucks (inefficient and costly), use cameras (static, can only cover so much area at once, and can be disable), or you have drones do that monitoring.

Here's how it works, in terms even a moron can follow: Agent GI Joe sits in his command center with a wall of cameras connected to drones flying around the border area. When he sees someone cross the border, he gets the A Team and they go round 'em up.

Each drone costs probably 1/10000th of what an area of actual wall that covers the same size would cost and does the same job. See how easy that is?