Every law student is given that speech. There used to be a specific scam targeting new lawyers. When a new law office was setup it would be sent books and lawyer-related equipment, along with a bill for payment. The scammers hoped the bill would just be paid without further inquiry. So law students are now warned and told that they can keep such "gifts".
But that isn't how the real world works. Who here doesn't have any previous contact with amazon? What if the package contains something very illegal (drugs etc) and the police are watching it? That will be a fun afternoon. Or what if your new address, previously perhaps a vacant house, is being used by someone buying illegal stuff? Yesterday he would pick it up from the door of an empty house. Today the package is inside the house. Unrequested deliveries should not be treated lightly.