This is all true, but the Grand Old Order of Locksmiths hasn't evolved this line of patter for no reason. Many people of my acquaintance are terrified of the po

This is all true, but the Grand Old Order of Locksmiths hasn't evolved this line of patter for no reason. Many people of my acquaintance are terrified of the possibility of burglars, even though home intrusions are very rare. Boosting people's confidence meaningfully improves their lives, even if 50% of the confidence boost is pure placebo effect. And physical locks do accomplish some things. They often require aspiring thieves to choose between speed and subtlety: Kicking open a door is fast but loud, picking a deadbolt is quieter but consumes a bit of time, and obviously both are slower and more obvious than opening an unlocked door. Physical locks protect against "misunderstandings". If you pass through a locked door and you don't have a key, you'll have a hard time convincing a cop or a judge that you were just making a mistake, or that "I saw the door standing open and was trying to investigate." Similarly, the "do not copy this key" message is not intended to be binding on locksmiths. It's a tiny contract between the landlord and the tenant, so if the tenant makes fifty copies of the key and hands them out at local bars, the landlord has clearer grounds for complaint. Finally, locks guard against crimes of opportunity. Not all of the world's aspiring thieves bother to learn lockpicking. Not all of them are sober enough to be very smart. And, as criminologists are fond of pointing out, a large percentage of crimes are committed by people the victim already knows, and there's a big social and psychological gap between "wandering into my cousin's house, seeing fifty bucks, and pocketing it" and "breaking down my cousin's door to look for fifty bucks."