I don't have a problem with locks on doors, it becomes a problem when kids either start playing with them (personal pet peeve) and if they deliberately and consistently lock me out and refuse to answer the door. Everyone needs privacy sometimes.
I've always found it hilarious that my oldest is the kid who is the most protective of his personal space and privacy, because he is also the kids who will barge into any closed door without a second thought. Lol, gotta love Aspies!