Masturbating is not the same as stealing a police car, nor is it bad for your health like smoking. When you describe the way you would approach the situation, why would you approach it like that? It sounds like the approach of a parent who loves their child and respects their right to bodily autonomy, but the response OP got from her mum was to act as if it's an abhorrent act to be controlled and stopped. Could you imagine doing that to your child and making them feel that way?