To harm a person = to diminish his prospects & adversely affect his possibilities
The principle of autonomy is consistent w/enforcement of morality à purpose: compare the scope & justification of Mill’s harm principle w/autonomy based freedom.
One harms another when his actions make him worse off than he was/is entitled to be in a way that affects his future well being, so if the govt. has a duty to promote autonomy of people, the harm principle allows it to use coercion both in order to stop people from actions which would diminish autonomy and in order to force them to take actions required to improve their options & opportunities.
Even if we aren’t directly causing harm; e.g. by not paying taxes, it’s still harm to un-assignable individual – one causes harm if one fails in his duty to a person/class of persons, and they suffer as a result. That’s so even if allocation of loss was determined by other hands (e.g. taxation).
So the harm principle allows full scope to autonomy based duties – a person who fails to discharge such duties towards others harms them, hence govt. whose resp. is to promote autonomy of citizens is entitled to redistribute resources, provide public goods & engage in provision of other services on compulsory basis, provided its laws reflect and make concrete autonomy based duties of its citizens.
Coercion is used to ensure compliance w/law and, if the law reflects autonomy based duties, then failure to comply harms others and principle of harm is satisfied.
Harm principle can be vindicated once interpreted not as restraint on pursuit of moral goals by the state but as indicating the right way in which it could promote the people’s well being. Given that they should lead autonomous life, state can’t force them to be moral but it can provide conditions for autonomy. Using coercion invades autonomy, thus defeating the purpose of promoting it, unless done to promote autonomy by preventing harm. Seen in this light, harm principle allowed perfectionist policies, so long as they dpnt require resort to coercion. The principle thus sets a necessary condition but doesn’t justify all uses of coercion to prevent harm.
A culture which doesn’t support autonomy yet enables its people to live an adequate & satisfying life should be tolerated, despite its scant regard for autonomy but it will be inferior to a liberal society. So long as they’re viable communities, offering acceptable prospects to their members, they should be allowed to continue in their ways.