A dupla face da proporcionalidade na tutela da vida: limites à força estatal e deveres de proteção na segurança pública a partir da ADPF 635

This article examines the dual face of proportionality, the prohibition of excess (Übermaßverbot) and the prohibition of insufficient protection (Untermaßverbot), in the protection of the right to life in the field of public security. The research adopts a theoretical and dogmatic approach and analyzes decisions of the Brazilian Federal Supreme Court issued between 2012 and 2025, with emphasis on ADPF 635, on police lethality, examined through the author’s reconstructive reading rather than as an application of the model declared by the Court. It argues that life holds a central position in the constitutional system because of its existential dimension, not because of an abstract normative superiority. Regarding excess, the rigid core of abstention is defined as the prohibition of death as the objective of state action: potentially lethal force is admissible only when strictly necessary to protect life or prevent serious injury from an imminent threat, and the intentional deprivation of life only when strictly necessary to protect another life, with no autonomous basis in the strict fulfilment of a legal duty. Regarding insufficiency, guiding criteria are proposed to identify deficient protection. Applying the proportionality test to the deployment of body-worn cameras indicates that the measure is suitable, necessary in view of the alternatives examined and proportionate, subject to conditions of regulation, data protection and funding. Judicial review of both faces is legitimate when reasoned, based on concrete demonstration of the excess or omission, and respectful of the competences and margin of choice of the responsible bodies. In criminal matters, the prohibition of insufficient protection does not authorize the judicial expansion of punitive power.