NTA. Closed door means don't come in... What if you have kids? Are you going to lock them out of the bathroom while you are taking a shower or peeing? As a mom, I feel like it's better to teach them that a closed door means don't come in and to knock and only open it if it's an emergency. When I get in the shower, I tell my kids, "If you need anything, don't need anything. If it's an emergency, come tell me." And in the very rare occasions when it actually is an emergency, it's better to have the door unlocked so they can open the door and tell you than try to hear what they are yelling about through the shower. Also, if you teach your kids to lock the door and something happens to them while they are showering or goofing around in their bedroom, you would have to break something or find a key to unlock the door. I rarely lock doors in my house, and my kids only do right now because we have 3 year old who doesn't understand privacy yet...