This assertion is just wrong. It's wrong in at least 4 ways, but I'm only going to give one, because I think you should be working this out on your own.
The reason people don't take advantage of the time when my door is open is because of the active security measures at that point. In particular, I am present, I represent a reasonable amount of security just by being present, and the law is also present. The reason that theft is rare is because theft is illegal, and confrontational, not because theft is hard.
People who want to burglar somebody's car or home are generally smart enough to wait until there isn't anybody in them, so I'm not sure what presence has to do with the issue. It's kind of beside the point of the analogy anyway. The point is if you can open a locked door with a valid key, a skilled person can get past the lock with their lockpicking tools, much as hackers can get through DRM. But in both cases, casual unauthorized access is prevented.
The reason people don't take advantage of the time when my door is open is because of the active security measures at that point. In particular, I am present, I represent a reasonable amount of security just by being present, and the law is also present. The reason that theft is rare is because theft is illegal, and confrontational, not because theft is hard.