Recent times have witnessed a multiplication of hypotheses of 'precautionary' interventions, which is to say a generalized anticipation of the moment when freedoms - from personal freedom to the right to privacy, from freedom of movement to freedom of expression - are curtailed in the name of security. The work focuses, as an element of a broader scenario that sees a clash between freedom and security, on a specific aspect: Can a democratic system, founded on the recognition of rights of liberty, opt for a 'preventive' system? Is it better to prevent or to repress? The topic is dealt with through the systematic and reasoned reconstruction of an interesting parliamentary debate that in the late nineteenth century involved Italian politicians and jurists in impassioned speeches hingeing on the 'prevent/repress' dichotomy and on the different versions of the concept of prevention.