What ethical dilemma is there? The law says no one can penetrate the United States except at designated border crossings. If the government thinks the best way to enforce that law is by a wall, what is unethical about that?

Many people seem to be confusing their political leanings with ethics, just because you personally are in favor of open borders doesn't make borders unethical, or even border walls.

The confusion of political opinions with ethics or morals is a much greater threat to the country. Once you define your own political position as the only ethical or moral one, and conclude that everyone who disagrees with you is an evil person, democracy can but collapse.