They're wetbacks. Instead of coming to the US legally like every American here did, they broke the law. They're criminals.
If someone kills another person, they are called a murderer, no? For breaking the law that says you can't murder people. If they broke the law that says you can't steal, they would be called thieves or robbers. If they broke the law that says you can't cross the US border without a green card, they would be called wetbacks.
Oh, and luis, unless you hop the fence on the border, we're not gonna call you a wetback.