There is an increasing call for preventive state interventions in so-called families at risk—that is, interventions before any overt harm has been done by parents to their children or by the children to a third party, in families that are statistically known to be liable to harm children. One of the basic principles of liberal morality, however, is the citizen's right to be free from state intervention so long as no demonstrable harm has been done. On the other hand, Joel Feinberg interprets the harm principle as a harm prevention principle, so that the risk of harm also might be a reason for interference. The question that needs to be asked, therefore, is whether enforced preventive intervention in the cases where families are judged to be at risk can be justified within the limits of liberalism.