We are in Orwell’s 1984 in many ways, and this is one of them. Controlling the language and how people use language also changes the ideas and concepts that can be expressed. If we can’t call these people illegal at all, it changes the concept of their status, so that the presumption is that there is no legal violation involved. If they are just “undocumented”, that puts them in the same category of somebody who is undocumented because he/she lost their driver’s license.