John Stuart Mill was one of the foremost liberal theorists of the 19th century, binding modern and classical liberalism in his ideas. His defence of liberty however, has been greatly contested by traditionalist views but also highly defended by revisionist views as will be examined in his paper On Liberty (1859). Mill's belief in individualism through utilitarian ethics appears contradictory and highly debated. His harms principle and his assumptions on human nature also submit to controversial views. On one hand, traditionalists condemn Mill as a highly inconsistent thinker and his work On Liberty very critical in itself, but on the other hand, revisionists see Mill as a consistent thinker who naturally refines and develops pre-existing liberal ideas.
J.S. Mill's father, James Mill, was a strong utilitarian theorist  . His beliefs along with the utilitarianism works of British philosopher Jeremy Bentham had a huge influence on J.S. Mill growing up  . In Mill's essay On Liberty, we can examine how his defence of individualism with utilitarian contentions create critical views. Mill believes in the ethic of utilitarianism in that the state and individuals ought to be judged by their ability and action to promote "the greatest happiness for the greatest number" of people  , however as traditionalists see it, attaining the utmost social good involves forfeiting certain individuals and sacrificing their happiness  , because happiness of a majority is greater than the happiness of a few individuals. Thus, the rudiment of utilitarianism is in dispute with Mill's beliefs in individuality and self-development.
In On Liberty, Mill defends freedom of the individual against "tyranny of the majority"  where dominant groups, more so the dominance of "public opinion", inhibits lesser individuals  . Mill's objection to the majority of society excluding the minority contradicts his utilitarian ethic. 19th Century English critic James Fitzjames Stephen condemns Mill's endeavour to defend individual liberty from a utilitarian viewpoint by arguing that, if the fundamental value for utilitarianism is to effectively enhance happiness of a society to the greatest extent, "then a consistent utilitarian policy of social betterment will not be especially tender toward individual liberty"  , the interest of the majority outweigh the rights of the individual minority. Stephen views that utilitarian principles pursues social welfare through restricting opinions of some members of society  and that individualism cannot be viewed with a utilitarian ethic J.S. Mill attempts to do.
On the other hand, revisionists argue that such traditionalist views are misinterpreted and that Mill's contradictions with utilitarianism is a "natural development of his utilitarian predecessors' achievements"  and his work not entirely incoherent. In Rem B. Edwards view, Mill is a minimizing utilitarian and that the principle of utility does not impose on individuals the moral obligation to maximize utility  , but focuses on happiness alone as the "ultimate standard of value" governing all human areas of practice.  In On Liberty, Mill regards utility "as the ultimate appeal on all ethical questions; but it must be utility in the largest sense, grounded on the permanent interests of a man as a progressive being."  That is to say, Mill's believes that utilitarianism is principle of the higher pleasures, and that freedom of choice, reflective thought and active imagination is a vital ingredient to human happiness.  For Mill, diversity of opinion leads to positive social good, therefore overlooking the minority and silencing their opinions deprives "the human race, posterity as well as the existing generation."  For revisionists, Mill as a utilitarian is not essentially inconsistent if he knowingly sacrifices some utility for the sake of a fair distribution of the utility that remains. 
J.S. Mill's notorious principle of liberty, the "harms principle" has also been disputed by traditionalist and revisionist views. In chapter four of On Liberty, Mill argues that people's actions ought not to be as free as opinions and should be limited if they are a "nuisance to other people"  . He states "that the only purpose for which power can be rightfully exercised over any member of a civilised community, against his will, is to prevent harm to others."  Traditionalist criticizes Mill's harm principle because Mill leaves room to suggest that it would be acceptable to limit liberty anytime if it could harm society in anyway. By making "harm to others" a legitimate reason for state interference, the legitimate powers of the state could extend and outweigh the need to value individuality. 
Another traditionalist indictment against Mill's principle of liberty is towards his account that actions should only be restricted if those actions are "other-regarding" and effect other people, and not if those actions are "self-regarding", which affect only the individual themselves and therefore should be exercised with absolute freedom  . The traditionalist criticize that we cannot clearly distinguish between the two actions Mill propose, as it is inevitable that people's actions affect others because people are not entirely secluded, therefore in theory any individual act can cause harm to others. As Fitzjames Stephen puts it, "I think that the attempt to distinguish between self-regarding acts and acts which regard others, is like an attempt to distinguish between acts which happen in time and acts which happen in space. Every act happens at some time and in some place, and in like manner every act that we do either does or may affect both ourselves and others. I think, therefore, that the distinction (which, by the way, is not at all a common one) is altogether fallacious and unfounded." 
In response to traditionalist criticism, revisionists attempt to clarify 'self-regarding' acts and 'other-regarding' acts. In J.C. Reese's essay, A Re-reading of Mill on Liberty, he distinguishes other-regarding actions to affect other people's interests in their moral rights, that of liberty and security.  Therefore, the "harm to others" implied in On Liberty refers to the harm of an individual's moral interests, resulting in injustice towards the individual.  As such, revisionist argue that 'self-regarding' actions can be clearly distinguished from 'other-regarding actions' and support Mill's harm principle in that actions can be restricted if they are injurious to the moral rights of security and liberty of other people.
The significant notion about human nature Mill makes in On Liberty, is how people can best understand and learn about their own opinions and activities from accepting challenging and opposing opinions and arguing against them. One can only faithfully understand their opinion by defending it.  This belief, based on the social utility of the individual is significantly disputed by traditionalists who argue people may not be able to best understand their opinions and values from dissent. For example, people who have different vocabulary for discussing moral and political issues may simply argue past each other, rather than challenge opposing opinions and therefore a diversity of opinions may not be socially beneficiary as it cannot increase utility, or happiness, which Mill defends as the essence of liberty.  Mill's claim about the need for dissent in order to truly understand one's own opinions is hereby less convincing.
It is easy to see how J.S. Mill's defence of liberty is highly contentious in views. As explained in this essay, Mill's prominent works such as On Liberty, gather traditionalist criticism as well as revisionist support. While traditionalists criticize Mill's defence of liberty from a utilitarian ethic, revisionists encourage us to respect Mill's work as a distinct process of developing liberalism. Mill refuses to accept fully the utilitarian principles inherited from his father and Bentham, nor reject them for his belief in 'individual sovereignty'  , but rather attempts to settle the two antagonistic viewpoints to defend liberty.