As we have noted in the past, Calvin allowed for the suppression of heretics for political reasons, but he did not believe that the faith could be coerced. One reason that it can not be coerced is that, for Calvin, worship must be offered willing. A worship give out of fear or force is of no value.
Calvin explains this in his Institutes, 1.4.4:
To this fault they add a second—viz. that when they do think of God it is against their will; never approaching him without being dragged into his presence, and when there, instead of the voluntary fear flowing from reverence of the divine majesty, feeling only that forced and servile fear which divine Judgment extorts Judgment which, from the impossibility of escape, they are compelled to dread, but which, while they dread, they at the same time also hate. To impiety, and to it alone, the saying of Statius properly applies: “Fear first brought gods into the world,” (Theb. lib. 1). Those whose inclinations are at variance with the justice of God, knowing that his tribunal has been erected for the punishment of transgression, earnestly wish that that tribunal were overthrown. Under the influence of this feeling they are actually warring against God, justice being one of his essential attributes. Perceiving that they are always within reach of his power, that resistance and evasion are alike impossible, they fear and tremble. Accordingly, to avoid the appearance of condemning a majesty by which all are overawed, they have recourse to some species of religious observance, never ceasing meanwhile to defile themselves with every kind of vice, and add crime to crime, until they have broken the holy law of the Lord in every one of its requirements, and set his whole righteousness at nought; at all events, they are not so restrained by their semblance of fear as not to luxuriate and take pleasure in iniquity, choosing rather to indulge their carnal propensities than to curb them with the bridle of the Holy Spirit. But since this shadow of religion (it scarcely even deserves to be called a shadow) is false and vain, it is easy to infer how much this confused knowledge of God differs from that piety which is instilled into the breasts of believers, and from which alone true religion springs. And yet hypocrites would fain, by means of tortuous windings, make a show of being near to God at the very time they are fleeing from him. For while the whole life ought to be one perpetual course of obedience, they rebel without fear in almost all their actions, and seek to appease him with a few paltry sacrifices; while they ought to serve him with integrity of heart and holiness of life, they endeavour to procure his favour by means of frivolous devices and punctilios of no value. Nay, they take greater license in their grovelling indulgences, because they imagine that they can fulfil their duty to him by preposterous expiations; in short, while their confidence ought to have been fixed upon him, they put him aside, and rest in themselves or the creatures. At length they bewilder themselves in such a maze of error, that the darkness of ignorance obscures, and ultimately extinguishes, those sparks which were designed to show them the glory of God.