It has absolutely nothing to do with being "politically correct." It has to do with keeping the taxpayers in the dark so they won't revolt and throw the bastards out of office when they find out how much the illegal aliens are costing. This is all about political power and control.
I am part of a local grassroots organization that lobbies on the Hill and state level. We have been pushing for more transparency in the costs of illegal immigration and the impact on our social welfare systems, schools, hospitals, law enforcement, etc. The ACLU, ethnic organizations like La Raza, the Catholic Church, and the Democrats have thrown up all kinds of roadblocks and obstacles using the smokescreen of privacy rights.
The Left knows that if the taxpayers learned the true costs, there would be hell to pay, especially now that state and local governments are cutting back on services and firing personnel.
You have hit the nail on the head.