For me it is not about locking us in, it's about locking out any potential trouble. I have had persons selling water heaters and alarm systems actually try to open my door when I didn't answer. Let me tell you they got an earful from me for that!!!! If my child was in daycare I would want to know the door is locked at all times after drop offs. They lock schools and daycare centres don't they?
I don't lock out of fear, just for security.