How can the idea of personal liberty survive the argument that we are all connected, so harm to oneself is harm to society? John Stuart Mill holds the line, strongly resisting the idea that the interconnectedness of people is an excuse for meddling. Only the actual harm we do to others–regardless of whether or not it is caused by harm to self–deserves blame or if severe, punishment. Here is his argument, from On Liberty, Chapter IV, "Of the Limits to the Authority of Society over the Individual” paragraphs 8-10:

The distinction here pointed out between the part of a person’s life which concerns only himself, and that which concerns others, many persons will refuse to admit. How (it may be asked) can any part of the conduct of a member of society be a matter of indifference to the other members? No person is an entirely isolated being; it is impossible for a person to do anything seriously or permanently hurtful to himself, without mischief reaching at least to his near connexions, and often far beyond them. If he injures his property, he does harm to those who directly or indirectly derived support from it, and usually diminishes, by a greater or less amount, the general resources of the community. If he deteriorates his bodily or mental faculties, he not only brings evil upon all who depended on him for any portion of their happiness, but disqualifies himself for rendering the services which he owes to his fellow-creatures generally; perhaps becomes a burthen on their affection or benevolence; and if such conduct were very frequent, hardly any offence that is committed would detract more from the general sum of good. Finally, if by his vices or follies a person does no direct harm to others, he is nevertheless (it may be said) injurious by his example; and ought to be compelled to control himself, for the sake of those whom the sight or knowledge of his conduct might corrupt or mislead.

And even (it will be added) if the consequences of misconduct could be confined to the vicious or thoughtless individual, ought society to abandon to their own guidance those who are manifestly unfit for it? If protection against themselves is confessedly due to children and persons under age, is not society equally bound to afford it to persons of mature years who are equally incapable of self-government? If gambling, or drunkenness, or incontinence, or idleness, or uncleanliness, are as injurious to happiness, and as great a hindrance to improvement, as many or most of the acts prohibited by law, why (it may be asked) should not law, so far as is consistent with practicability and social convenience, endeavour to repress these also? And as a supplement to the unavoidable imperfections of law, ought not opinion at least to organize a powerful police against these vices, and visit rigidly with social penalties those who are known to practise them? There is no question here (it may be said) about restricting individuality, or impeding the trial of new and original experiments in living. The only things it is sought to prevent are things which have been tried and condemned from the beginning of the world until now; things which experience has shown not to be useful or suitable to any person’s individuality. There must be some length of time and amount of experience, after which a moral or prudential truth may be regarded as established: and it is merely desired to prevent generation after generation from falling over the same precipice which has been fatal to their predecessors.

I fully admit that the mischief which a person does to himself may seriously affect, both through their sympathies and their interests, those nearly connected with him, and in a minor degree, society at large. When, by conduct of this sort, a person is led to violate a distinct and assignable obligation to any other person or persons, the case is taken out of the self-regarding class, and becomes amenable to moral disapprobation in the proper sense of the term. If, for example, a man, through intemperance or extravagance, becomes unable to pay his debts, or, having undertaken the moral responsibility of a family, becomes from the same cause incapable of supporting or educating them, he is deservedly reprobated, and might be justly punished; but it is for the breach of duty to his family or creditors, not for the extravagance. If the resources which ought to have been devoted to them, had been diverted from them for the most prudent investment, the moral culpability would have been the same. George Barnwell murdered his uncle to get money for his mistress, but if he had done it to set himself up in business, he would equally have been hanged. Again, in the frequent case of a man who causes grief to his family by addiction to bad habits, he deserves reproach for his unkindness or ingratitude; but so he may for cultivating habits not in themselves vicious, if they are painful to those with whom he passes his life, or who from personal ties are dependent on him for their comfort. Whoever fails in the consideration generally due to the interests and feelings of others, not being compelled by some more imperative duty, or justified by allowable self-preference, is a subject of moral disapprobation for that failure, but not for the cause of it, nor for the errors, merely personal to himself, which may have remotely led to it. In like manner, when a person disables himself, by conduct purely self-regarding, from the performance of some definite duty incumbent on him to the public, he is guilty of a social offence. No person ought to be punished simply for being drunk; but a soldier or a policeman should be punished for being drunk on duty. Whenever, in short, there is a definite damage, or a definite risk of damage, either to an individual or to the public, the case is taken out of the province of liberty, and placed in that of morality or law.

Notice that this principle means that excusing one’s behavior by reduced capacity from, say, alcohol use, or not having gotten enough sleep, should not be given much weight. If allowing one’s capacity to be reduced is likely to lead one to harm others, one has the responsibility to avoid reducing one’s capacity when in the presence of others one might hurt.

In other words, allowing people freedom in their private lives means that we should allow fewer excuses for the effects of their interactions with others.