The principal end of punishment in the United States

See Hallam’s Constitutional History and Speech on the Government of India

“That, on great emergencies, the State may justifiably pass a retrospective act against an offender, we have no doubt whatever. We are acquainted with only one argument on the other side which has in it enough of reason to bear an answer. Warning, it is said, is the end of punishment. But a punishment inflicted, not by a general rule, but by an arbitrary discretion, cannot serve the purpose of a warning. It is therefore useless; and useless pain ought not to be inflicted. This sophism has found its way into several books on penal legislation. It admits, however, of a very simple refutation. In the first place, punishments ex post facto are not altogether useless even as warnings. They are warnings to a particular class which stand in great need of warnings, to favourites and ministers. They remind persons of this description that there may be a day of reckoning for those who ruin and enslave their country in all the forms of law. But this is not all. Warning is, in ordinary cases, the principal end of punishment; but it is not the only end. To remove the offender, to preserve society from those dangers which are to be apprehended from his incorrigible depravity, is often one of the ends. In the case of such a knave as Wild, or such a ruffian as Thurtell, it is a very important end. In the case of a powerful and wicked statesman, it is infinitely more important; so important as alone to justify the utmost severity, even though it were certain that his fate would not deter others from imitating his example. At present, indeed, we should think it extremely pernicious to take such a course, even with a worse minister than Strafford, if a worse could exist; for, at present, Parliament has only to withhold its support from a Cabinet to produce an immediate change of hands. The case was widely different in the reign of Charles the First. That Prince had governed during eleven years without any Parliament, and, even when Parliament was sitting, had supported Buckingham against its most violent remonstrances.”

Lord Thomas Babington Macaulay: Hallam, Sept. 1828.