This would eliminate the possibility of them having another baby (and extend it to adopting or fostering) and putting that child at risk of harm. It would also save endless resources being spent on monitoring the situation. Zero tolerance where children's lives are at stake, surely.
I would like to see a system in place whereby people convicted of serious crimes against children – for example Karen Matthews and the three adults involved in the death of Baby Peter – are sterilised upon conviction. They have had children, abused those children and should therefore forfeit the right to have any more. Too often in these cases, the authorities are vilified by the media and the public (let's blame social services, the police, the school etc) and we overlook that the parents or guardians of these children are ultimately responsible for the crime. Let's learn from our mistakes by all means, and improve our procedures and systems, but let's also never ever give people the chance to put another child through this.