It seems to me that there is already a nation in the world that has such a system in place, one that doesn't want the people from the south to enter their worker's paradise in the north, one that is satisfyingly authoritarian. No doubt it would be worth emulating that nation.
Can't we just turn Congress off and then turn it back on again?
Furthermore, the constitution prohibits use of deadly force except as reasonably nessecary to preserve life (Garner v. Tennessee) and the Constitutional protections apply to aliens as well as citizens.
people go up to the border all the time. there's towns that literally touch the border, your kill team going to execute the entire population of Nogales? cemetaries, missions, other historic sites are located on the border, and the areas on the border are popular with hikers, backpackers etc. your idea is a stupid one. and it's totally illegal.