SEATTLE, May 24 — To build, or not to build, a border of walls? The debate in the United States has started some Mexicans thinking it is not such a bad idea. Nationalist outrage and accusations of hypocrisy over the prospect have filled airwaves and front pages in Mexico, as expected, fueled by presidential campaigns in which appeals to national pride are in no short supply. But, surprisingly, another view is gaining traction: that good fences can make good neighbors. The clamorous debate over a border wall has confronted President Vicente Fox of Mexico at every stop during a visit...