But imagine if you only locked your front door and left your back door completely unlocked all the time. The front door lock would stop honest visitors from entering your home, but they probably didn't need to be stopped anyway, because they would knock before entering. Whereas criminals will neither knock nor use the front door.
We're totally in agreement regarding TCC, but this analogy has a lot of issues. A criminal could also break a window, or—even easier—pick the lock, because the locks on most houses can be trivially broken.
There's a couple reasons locks work IRL despite this, one of which is that they don't really stop honest visitors. You don't usually want anyone coming into your house that you haven't let in yourself, unless they're family members with keys.
Yeah, I don't think these "door lock" analogies are helpful for either side of the argument. The situation with a computer operating system is not analogous.