The wall wont do shit. No matter how many people die at the hands of an illegal immigrant a wall wont stop them from getting into the country. Thats like putting a wall around a building with tons of gold and expecting no one will ever climb over it.
I'm not sure if your reference to Fort Knox is meant to be funny, and I don't know if anyone has ever gotten in.
But your point is true to a tiny point. Walls don't eliminate illegal immigration. Similarly, walls around prisons don't eliminate escapes, but we build them anyway, because they
work, that is, they reduce escapes to a manageable rarity.
Of course, we don't have a national political Party dedicated to helping prisoners escape, providing way stations and advice, calling for an end to prison guards, and most especially providing sanctuary to escapees, etc., with sympathetic media coverage. That would be fun.