What are you going to do, go door to door in LA rounding them all up and forcibly putting them on trucks? Good idea, Registered! What about their belongings? What about the sick and frail? Children? That will make such good TV footage that we will never elect a conservative again!
By the way, you could take ALL police and INS agents in the LA area and you STILL wouldn't be able to do it. Plus, it would require checking EVERY house and asking to "see people's papers." Sounds a bit impractical and totalitarian to me.