Let us use our own brains a little, and ask ourselves what is the real difference between punishing a man and restraining him. The material difference may be any or none; for punishment may be very mild, and restraint may be very ruthless. The man, of course, must dislike one as much as the other, or it would not be necessary to restrain him at all. And I assure you he will get no great glow of comfort out of your calling him irresponsible after you have made him impotent. A man does not necessarily feel more free and easy in a straight waistcoat than in a stone cell. The moral difference is that a man can be punished for a crime because he is born a citizen; while he can be constrained because he is born a slave. But one arresting and tremendous difference towers over all these doubtful or arguable differences. There is one respect, vital to all our liberties and all our lives, in which the new restraint would be different from the old punishment. It is of this that the plutocrats will take advantage.
The perfectly plain difference is this. All punishment, even the most horrible, proceeds upon the assumption that the extent of the evil is known, and that a certain amount of expiation goes with it. Even if you hang the man, you cannot hang him twice. Even if you burn him, you cannot burn him for a month. And in the case of all ordinary imprisonments, the whole aim of free institutions from the beginning of the world has been to insist that a man shall be convicted of a definite crime and confined for a definite period. But the moment you admit this notion of medical restraint, you must in fairness admit that it may go on as long as the authorities choose to think (or say) that it ought to go on. The man’s punishment refers to the past, which is supposed to have been investigated, and which, in some degree at least, has been investigated. But his restraint refers to the future, which his doctors, keepers, and wardens have yet to investigate.
— Utopia of Usurers (1917).