Mill imparts an optimistic, if cautious, mood onto the reader in "On Liberty. " He is clear that humanity is capable of great and wonderful things, as in his long discussions on genius and individuality, but he is troubled by the infinite potential for society and government (and the authorities therein) to limit the human mind and the human spirit. This concern rubs off on the mood of his essay—he even ends his work with a warning to the State itself:
...a State which dwarfs its men, in order that they may be more docile instruments in its hands even for beneficial purposes—will find that with small men no great thing can really be accomplished; and that the perfection of machinery to which it has sacrificed everything will in the end avail it nothing, for want of the vital power which, in order that the machine might work more smoothly, it has preferred to banish.
As much as this passage is a warning to the reader about the dangers of government overreach and authoritarianism, it also contains a note of inspiration: "small men" may not be able to accomplish anything, but, left to its own devices, humanity will produce greatness. And if we protect the liberties of individuals, they will be free to think great thoughts and do great things.