You can't show up with thugs and take something you don't know exists. Sure you could go door to door looking for whatever your after (be that people or proper

You can't show up with thugs and take something you don't know exists. Sure you could go door to door looking for whatever your after (be that people or property) but that scales inefficiently and the false positive rate will be so high it will probably provoke a revolt. In practice registration is a necessary precursor to the government showing up and taking something unless the government can get people's neighbors to rat on each other (good luck with that). Governments have killed a lot of people and stolen a lot of property over the years. People are justified in being very weary of the government knowing who they are and what they have. The first 20yr of the USSR are probably a better point of comparison than the holocaust but whatever.