John Stuart Mill
The only contingency upon Mill's harm principle is that the person involved has to be capable of making their own decisions if the action might harm them. Mill gave an example to illustrate this dilemma; a person is about to cross a broken bridge from which they will surely fall to their death, you may feel inclined to stop them, however all you can do is warn them of the consequences of crossing. If they are making a rational choice to die then you must allow them to continue. Mill goes on to say, however, that if the person is "a child, or delirious, or in some state of excitement or absorption incompatible with the full use of the reflecting faculty" (Mill, pp.173) then we are morally obliged to stop them.
This means that as long as the person performing the action is an adult who is capable of making their own decisions, then the government should have no power over any activity that does not impair the rights of others. Mill argued that this freedom would increase the utility of all mankind because it would encourage people to find the best life to lead for themselves. Mill felt very strongly that people would be happier if they were free from the demands of social conformity which he believed to be a symptom of democracy and capitalism.
Mill stated that; "society can and does execute its own mandates; and if it issues wrong mandates instead of right, or any mandates at all in things with which it ought not to meddle, it practices a social tyranny more formidable than many kinds of political oppression, since, though not usually upheld by such extreme penalties, it leaves fewer means of escape, penetrating much more deeply into the details of life, and enslaving the soul itself" (Mill, pp.13). French philosopher Alexis De Tocqueville first discussed this problem in 1839. He stated that "the sovereign can no longer say, 'You shall think as I do on pain of death'...he says, 'You are free to think differently from me, and to retain your life, your property, and all that you possess; but if such be your determination, you are henceforth an alien along your people'" (De Tocqueville, pp.338).
If Mill's theory were actualised then people would be encouraged to explore "experiments of living", there would be a large variety of schools, religions and local political systems. Any behaviour between consenting adults would be legal in specified places such as your own home and even if a certain experiment in living has been found to fail over and over again, people should still be allowed to try it. If they were not then Mill argued that this would have many implications that would decrease mankind's utility. It would increase the power of the government, something Mill severely wished to avoid, but most importantly people would not be able to understand why a certain experiment in living was wrong if it had been banned for such a period of time that they became "dead dogma," instead of "living truth" (Mill, pp.64).
Mill argued that everyone should be entitled to free speech, even hate speech, because if it is correct then society needs to hear it and if it false then it is important that we understand why it is false. Mill stated that; "If all mankind minus one, were of one opinion, and only one person were of the contrary opinion, mankind would be no more justified in silencing that one person, than he, if he had the power, would be justified in silencing mankind" (Mill, pp.33). To do so would be to assume infallibility. History shows we are fallible and that it is only through 'radical' movements, for which speech can be very important, that we are able to progress.
In 1959, English judge Lord Patrick Devlin opposed this view, arguing that utility would be improved if actions such as recreational drug taking, prostitution and homosexuality, were banned (Delvin, 1989). This is because he believed society has a right to protect its shared morality. Mill would argue that the abstract idea of 'society' has no value or rights, there are only individuals who should lead individual lives. The evolution of society has progressively involved giving more rights to the individual and the utility Mill speaks of is utility over a long period of time for all of humanity.
References
Mill, J.S., 1869, 'On Liberty', Longmans, Green, Reader, & Dyer, London