A theory I have no reason to believe on the basis of your say so.
However, my position is to build a wall. I do thank you for noting my intent isn't only to focus on Mexico. IMO, too many directly focus solely there just because that is where the greatest number enter.
On this you are correct.
The reason being it's a permanent barrier a politician safely re-lected or a new administration cannot easily dismantle. It's not the only thing that must be done, disincentives must be applied from within but it's a concrete barrier that will slow traffic at least.
If our government had earned trust on the matter, I would be more lenient and might even accept "virtual" fences or just more troops on the border or more border guards.
The heart of the matter is that I don't trust them on this. neither do many, that's why insistence on the wall.