Undocumented immigrants can have authentic, non-"RealID" ids, as things such as drivers licenses are the purview of the states, and infringement there upon is an attack on their constitutional sovereignty. California, for example, is perfectly happy to give out drivers licenses to anybody who can establish residency and pass the test, since there's no sense in creating a double jeopardy situation wherein because someone has committed one crime (illegally immigrating to California), they are forced to commit an additional crime (driving without a license). It's the same reason the IRS gives you a spot to declare your bribes and other illegal income.

What exactly makes RealID more secure than the drivers license my state has issued for the last 20 years?