Pacem in Terris §48

⁴⁸ Hence, a regime which governs solely or mainly by means of threats and intimidation or promises of reward, provides men with no effective incentive to work for the common good. And even if it did, it would certainly be offensive to the dignity of free and rational human beings. Authority is before all else a moral force. For this reason the appeal of rulers should be to the individual conscience, to the duty which every man has of voluntarily contributing to the common good. But since all men are equal in natural dignity, no man has the capacity to force internal compliance on another. Only God can do that, for He alone scrutinizes and judges the secret counsels of the heart.