We are talking about "foreign nationals who live without official authorization in a country of which they are not a citizen." Many of these nationals are documented but they do not reside here legally. Illegal immigrant is a more accurate term than undocumented immigrant. An alien is any individual who is not a U.S. citizen or U.S. national. We are referring to aliens residing in the country illegally, hence the appropriate term 'illegal alien.'
Take your love of ever changing neutral terminology and shove it up the exhaust manifold of your posterior sitting region. Don't be a bigot against truthful terms.