The term “illegal alien” is loaded with a presumption of criminal guilt.
In contrast, “undocumented worker” is a neutral description of the situation of people who are in the United States without papers proving their legal status.
If an immigration court were to hear their cases, it might conceivably uphold their right to be here.
“Illegal alien” is even worse than “illegal immigrant.” The term “alien” sounds like a monster from a science fiction movie, like the 1997 movie Men in Black, in which the “illegal aliens” were just that.