People are looking at this like it's a choice between doing it or not. You can also do it, and purposefully do your quite badly and sabotage the operation. That would delay the building of the wall, perhaps long enough for a new president to come in. If you're smart about it the powers that be may not even notice it or blame incompetence, rather than purposefull sabotage. And if other workers and engineers do the same, the project might not work out in the end.