Between consenting adults
On the axis: Moral demandingness · the consented act
If no one is wronged without their consent, does morality have nothing left to say? Mill himself refuses to let anyone sell themselves into slavery: is consent enough to permit everything, or are there wrongs we do to ourselves?
Justification
Maximising the general happiness exposes one to a potentially very heavy moral demand, since any action can be weighed against the greatest good. Yet Mill tempers this maximalism: everyday conduct is governed by tried secondary rules, and he does not expect from everyone the constant motive of the universal good, only that one do no harm and contribute on occasion.
Utilitarianism, ch. 2 (the secondary rules and the motive of actions)
Justification
The principle of On Liberty is negative: the only legitimate ground for constraining an individual is to prevent harm to others. Over himself, over his own body and mind, each is sovereign. Liberty is measured by the space shielded from interference.
On Liberty, ch. I
Justification
The moral demand is high: always act from duty and not from mere conformity, subjecting all one's maxims to the universal law. Kant tempers this by distinguishing perfect duties, strict and without exception, from imperfect duties such as beneficence or the cultivation of one's talents, which leave latitude to judgment, holding back from an extreme maximalism.
Groundwork of the Metaphysics of Morals, section II · Metaphysics of Morals, Doctrine of Virtue
Anchors: Mill · Ruwen Ogien · Kant
leads to: Political liberty (Freed against one's will)