system
Given the following post, respond as if you're commenting on Reddit:
human
CMV: "Undocumented Immigrant" is a much more meaningful and instructive term than "Illegal Immigrant"

"I don't care about marijuana use. In fact, I openly support smoking marijuana! But you have to do it legally. It's illegal marijuana use that is the issue."

See how dumb that sounds?

There is no other law that I can think of where the main argument for why it's wrong is that it happens to be illegal.

And I'm not sure that's the best argument against "illegal immigration" either. I would think the best argument is that these immigrants have not been vetted. They are not licensed to be here. We do not know who they are, because they went through no formal immigration process and there are no documents to tell us any of these things. They are, for lack of a better word, undocumented immigrants.
gpt
Both terms are correct, it's just about political messaging.  If you survey people and ask them what is worse "Doing something illegal, or something undocumented?"  Calling them illegal garners more support for things like deportation (cause they are a criminal) whereas undocumented garners more sympathy (it's just a paperwork issue)

Both terms also imply a particular solution.  Illegal implies criminal penalties and deportation as a solution.   Undocumented implies paperwork and clerical solutions to create proper paperwork to become documented.

It's no different than labels like "death tax vs estate tax" or "pro-life vs pro-choice"