The corporations don't want to run out of desperate people who will work in factories for peanuts. Americans are too much trouble and demand "rights" which are inconvenient.
Why does your house have walls? Do you keep your door closed? Does it have a lock? Should anyone be allowed to come into your home uninvited? Should they be allowed to come into your home and stay there without your permission? Should you be then forced to also pay for those uninvited people to stay in your home? You wouldn’t tolerate that for a moment. So why should we as a country tolerate it?
People see undocumented immigration as a problem. Maybe to them it's a national security threat, or as an insult to American law, or they have the perception that the people crossing the border this way are violent criminals or drug dealers.
There's definitely nuggets of truth in all that, which solidifies the argument for proponents of the wall, but the majority of the data out there doesn't really back up these narratives.
You can make the argument that it's better to keep out everybody on the chance that some people might actually do grievous harm to the nation or people in it. So through that lens, it's worth the effort.
Personally, just doing a cost-benefit analysis will show it's a complete waste of money. A wall might give the illusion of security, and for a lot of people that's good enough, but it's basically just political theatre when you look at the numbers.
@JimBeam You're the example they use when people are warned not to argue with idiots. You contribute nothing, you refuse to learn anything, and you argue things that are at best tangentially related to the topic at hand.
I'm done with you. You've earned your block. Now you're free to go be an idiot somewhere else
