Tell me why banks and White House have a fence? Would it be easier just to shoot people?
Anyway, it is unlikely that army would shoot illegals. Old-fashioned fence works very well in Israel (and Mexico has that too on its southern border). Now you can simply walk into the US (whether you are a child, old lady etc). If we have a wall, it is much easier to control the border. In San Diego area, illegal entries dropped to almost zero after the wall.
Fence works. People who claim otherwise arre amnesty frieks who use whatevery excuse possible to advance amnesty.
First off, none of my banks have a fence, and second the White House fence covers one city block. Fences have their applications, but imho the entire southern border of the US is not one of them. I maintain an Isreali manufactured Yael 15 fence for my employer. The cost of replacing one sensor and PCB is almost $7000. Our fence is only 2.2 miles long, and you want to build one 1200 miles long. Trust me, if you don't monitor the fence with troops anyway, it will be defeated in short order.