Walls keep people in as well as out. If Mexico pays in full for a wall, it will want total control of it. Currently, the border maintenance and operation is based on co-functioning of Mexico with the US and is a border “zone” about a hundred and twenty miles deep. A wall paid for by Mexico would be potentially a containment wall for Americans based on policy determined by Mexico alone. One cannot expect that Mexicans would be kept out and Americans not kept in.
“One cannot expect that Mexicans would be kept out and Americans not kept in.”
Why would the average American care?