Duty and Coercion

I was looking in Mill's Utilitarianism for relationships of his discussion of justice to Cicero's, and found this remarkable passage:

For the truth is, that the idea of penal sanction, which is the essence of law, enters not only into the conception of injustice, but into that of any kind of wrong. We do not call anything wrong, unless we mean to imply that a person ought to be punished in some way or other for doing it; if not by law, by the opinion of his fellow-creatures; if not by opinion, by the reproaches of his own conscience. This seems the real turning point of the distinction between morality and simple expediency. It is a part of the notion of Duty in every one of its forms, that a person may rightfully be compelled to fulfil it. Duty is a thing which may be exacted from a person, as one exacts a debt. Unless we think that it may be exacted from him, we do not call it his duty. Reasons of prudence, or the interest of other people, may militate against actually exacting it; but the person himself, it is clearly understood, would not be entitled to complain. There are other things, on the contrary, which we wish that people should do, which we like or admire them for doing, perhaps dislike or despise them for not doing, but yet admit that they are not bound to do; it is not a case of moral obligation; we do not blame them, that is, we do not think that they are proper objects of punishment. How we come by these ideas of deserving and not deserving punishment, will appear, perhaps, in the sequel; but I think there is no doubt that this distinction lies at the bottom of the notions of right and wrong; that we call any conduct wrong, or employ, instead, some other term of dislike or disparagement, according as we think that the person ought, or ought not, to be punished for it; and we say, it would be right, to do so and so, or merely that it would be desirable or laudable, according as we would wish to see the person whom it concerns, compelled, or only persuaded and exhorted, to act in that manner. (My emphasis.)

Now I don't think there is anything like this in Cicero. For Cicero, I believe, a duty is a sort of action which makes a claim on us, as having to be done, in virtue of our being rational creatures. It is a requirement of reason, which does not carry along with it, inevitably, any suggestion of coercion by another. (Compare: "Given that you have written, 'All horses are mammals', and 'All mammals are endothermic', the conclusion needing to be written is 'All horses are endothermic'." --But there is no thought here of our being ready to compel the person to write that conclusion. Rather, it seems that the use of compulsion here would be self-defeating; it would destroy what we were aiming to foster.)

Of course if duty carries along with it necessarily the condition that another may rightfully compel, then one will want to minimize the reach of duty, as Mill does in On Liberty. Here too is a contrast with Cicero, who rather wants considerations of officium to enter into everything that we do, every action and choice, since that serves to make our life more rational.