One aspect of Mill's argument that struck me is the tyranny of the majority. The idea is that strong democracy prevents tyranny by a single despotic ruler, but does not prevent the oppression of a minority group by the majority.
Like other tyrannies, the tyranny of the majority was at first, and is still vulgarly, held in dread,.... Protection, therefore, against the tyranny of the magistrate is not enough; there needs protection also against the tyranny of the prevailing opinion and feeling, against the tendency of society to impose, by other means than civil penalties, its own ideas and practices as rules of conduct on those who dissent from them; to fetter the development and, if possible, prevent the formation of any individuality not in harmony with its ways, and compel all characters to fashion themselves upon the model of its own. (On Liberty, Introduction, Page 3)
So, what made me think about this? Washington, D.C.'s battles with gay rights. Some folks in D.C. wanted to put the city's same-sex marriage law (which was approved by the City Council and signed by the Mayor) to a referendum vote.
Ultimately, these people failed. Still, it worried me that they thought they had any chance. The idea that putting something to referendum is always the answer is wrong-headed. John Stuart Mill was talking about just this sort of thing. What if Lincoln had put the Emancipation Proclamation to a referendum vote? What about the Civil Rights Act of 1964? When the majority use a referendum to impose their opinions on minority groups, it is morally reprehensible.