The more common phrase, ‘‘illegal immigrant,’’ also implies suspicion, but strip the noun from it and the entire identity of a person who crosses the border without permission, or outstays his or her visa, is reduced to that of a criminal: What rights could he or she be entitled to? ‘‘Illegals’’ becomes the noun, the insult and the dismissal. Designating immigrants as ‘‘illegals’’ also makes it easier not to see the frequent lawbreaking of employers who provide meager pay and unsafe working conditions. And ‘‘illegals’’ implies a permanent caste, as if there is no possibility of becoming anything else — even if millions of immigrants in the course of American history have shown otherwise. [The Unwelcome Return Of 'Illegals' by Emily Bazelon; New York Times Magazine, August 18th 2015.]The fun here is in reading the comments to Ms Bazelon's column. Not even New York Times readers are buying the "undocumented" baloney nowadays.
(Before the "undocumented" sleight of pen was cooked up, the usual thing was to refer to illegal aliens as "illegal aliens," i.e. with hatequotes. I was grumbling about this back in October of 2000.)