John Stuart Mills

From here:

But if we want to be more confrontational, we could use what I like to call the "On Liberty argument" from John Stuart Mill's most famous essay. The argument essentially accepts a certain degree of skepticism about truth and absolute rights and wrongs. According to Mill, that commits you to a very healthy set of civil liberties. Since one can never be sure about the eternal truth of certain propositions, then one cannot be justified in silencing and oppressing others because they possess certain ideas or cultural identities. Conversely, you cannot justify oppressing people because you possess certain ideas of cultural identities. So you are committed to a free and open forum of clashing ideas and ruthless argument. This amounts to an inviolable sphere where people are free to pursue their own projects and their own truths, which is the liberal project (and the ideal of rights discourse in the first place) anyway. A healthy skepticism about truth, in this case, motivates the move towards human rights. So we find that the idea of human value and inviolability has a powerful intuitive hold on us, that such conceptions are central to who we are, and that even skepticism points to the formulation of basic human liberty. It seems that we have good reasons to reject this combination of rights and multiculturalism.