A wall cannot substitute for well-crafted changes in immigration law.
Not meant to substitute, meant to supplement laws.
No one can deny that a 30' wall is a deterrent to most and will at least slow down the flow of even the hardiest illegal.
The walls are sensitized and eyeballed via drone, so even if breached, the BP will be able to get there in time to stop illegal entry.
Nothing is 100% fool proof, but there are walls around jails for a reason, and there are walls around rich homes and gated communities for the same reason.