When one refers to an immigrant as an "illegal alien," one is using the term as a noun. The user of the term is effectively saying that the individual, as opposed to any actions that the individual has taken, is illegal. The term “illegal alien” implies that a person’s existence is criminal. I’m not aware of any other circumstance in our common vernacular where a crime is considered to render the individual – as opposed to the individual’s actions – as being illegal. We don’t even refer to our most dangerous and vile criminals as being “illegal” people.
