Even if we pretend this is only about drug smuggling (strawman), I'd say forcing smuggler to dig a tunnel or build a submarine or raft is a substantial deterrent as compared to walking. I know I've never personally bothered to tunnel under a wall. You know why they resort to tunnelling? Because of the rough ridin' wall.
I honestly don't give a crap if they build this wall, but to act like a wall isn't an effective way to keep people out is batshit rough ridin' crazy. It's like saying a roof isn't good at blocking sunlight, because windows.