I've taught the main idea of John Stuart Mill's "On Liberty" before--in introductory level courses. I've taught his separation of cases argument against government suppression of free speech. And I've taught Liberty in a way that incorporates a discussion of freedom of action and specifically victimless crimes.
But one of the questions that I had, going into teaching this course, is whether "Liberty" is supportive of the variety of political thought that in the news media gets called libertarianism.
I'm far from an expert on contemporary libertarianism. I know that it comes in liberal and conservative flavors, and that libertarians from the right and from the left sometimes find mutual support. Libertarianism.org, for example, houses information about Mill, and The Liberty Fund archives Mill's collected works at http://oll.libertyfund.org/?option=com_staticxt&staticfile=show.php%3Fcollection=46&Itemid=27.
In my course, one very good and politically engaged student was conservative but had mixed commitments to libertarianism and communitarianism. He was mostly supportive of Mill's ideas and, when critical, usually viewed Mill's philosophy as tending to undermine social order and tradition. Another student was liberal in a distinctly libertarian way. He, too, found that Mill's political philosophy fit his own ideals.
But after a close reading of "On Liberty" and of some of Mill's other works, I have a difficult time seeing how Mill's commitments can provide the basis for contemporary conservative libertarians who would like to see less government, a reduction in government entitlements (usually with no reduction in government support for corporations), and a very low taxation rate and regressive tax scheme. Mill even seems amenable to limiting civil liberties in some cases if it is in the long-term interests of society.
In fact, Mill's individualism seems nearly completely secondary to his collectivism. The reason he supports individualism is for the very good reason that the way to develop the greatest potential in society is to develop the potential of its individual members. For example, he supports compulsory education at a time when it was controversial in England. And he is against limiting the choices that individuals make because in doing so we limit our possibilities for future growth. We should allow people to make mistakes because some of the different and unusual ideas they develop in their experiments in living will be better for society as a whole.
This is far from selfishness or egoism, and it is also far from saying that government has no business in people's private lives. The state does have an interest in how people develop their private lives, and its interest is to clear the way of obstacles to having the widest possible range of choices in how to live (so long as people's choices do not harm others). The state has this interest because WE are the state--the commitment to participatory democratic governance is simple and straightforward. Further, there even seems to be a duty (or a consideration of beneficience, at least) to GIVE BACK to society, or to develop oneself for the sake of benefitting others, including the people of the future.
I had wondered if the individualism of "Liberty" was in conflict with the collectivism of "Utilitarianism." I think the relationship is this: an iron-clad commitment to the liberty of individuals is a pre-requisite to developing a society with the greatest sum total of happiness, and especially for the development of higher pleasures. One needs both freedom and security in order to write poetry. Mill comes back again and again to the idea that society has, can, and will progress. But that progress is built on two things: first, that people have liberty to change their lives in ways that are an improvement over past ways of living; and second, that they are motivated to develop and build the society, as a collective, rather than (just) to tend their own self-interests.