Christians, like all people of good will, are called upon under grave obligation of conscience not to cooperate formally in practices which, even if permitted by civil legislation, are contrary to God's law. Indeed, from the moral standpoint, it is never licit to cooperate formally in evil. Such cooperation occurs when an action, either by its very nature or by the form it takes in a concrete situation, can be defined as a direct participation in an act against innocent human life or a sharing in the immoral intention of the person committing it. This cooperation can never be justified either by invoking respect for the freedom of others or by appealing to the fact that civil law permits it or requires it. Each individual in fact has moral responsibility for the acts which he personally performs; no one can be exempted from this responsibility, and on the basis of it everyone will be judged by God himself (cf. Rom 2:6; 14:12). To refuse to take part in committing an injustice is not only a moral duty; it is also a basic human right. Were this not so, the human person would be forced to perform an action intrinsically incompatible with human dignity, and in this way human freedom itself, the authentic meaning and purpose of which are found in its orientation to the true and the good, would be radically compromised. What is at stake therefore is an essential right which, precisely as such, should be acknowledged and protected by civil law. In this sense, the opportunity to refuse to take part in the phases of consultation, preparation and execution of these acts against life should be guaranteed to physicians, health-care personnel, and directors of hospitals, clinics and convalescent facilities. Those who have recourse to conscientious objection must be protected not only from legal penalties but also from any negative effects on the legal, disciplinary, financial and professional plane. (Papal Encyclical, Evangelium Vitae, 25 March 1995).
But, to judge aright, we must acknowledge that, the more a State is driven to tolerate evil, the further is it from perfection; and that the tolerance of evil which is dictated by political prudence should be strictly confined to the limits which its justifying cause, the public welfare, requires. Wherefore, if such tolerance would be injurious to the public welfare, and entail greater evils on the State, it would not be lawful; for in such case the motive of good is wanting. (Papal Writings, Libertas, 1888).