“When laws, customs, or institutions cease to be beneficial to man, they cease to be obligatory.”

The Spirit of Christianity and its Fate (1799)

No. 63.
Aphorisms (1930)

Variant: When a man cannot choose, he ceases to be a man.
Source: A Clockwork Orange

.
Memoirs (trans. Machen 1894), book 1, Preface http://etext.library.adelaide.edu.au/c/casanova/c33m/preface2.html
Referenced

Variant translation: Liberal institutions straightway cease from being liberal the moment they are soundly established: once this is attained no more grievous and more thorough enemies of freedom exist than liberal institutions.
Expeditions of an Untimely Man, 38
Twilight of the Idols (1888)
Context: My conception of freedom. — The value of a thing sometimes does not lie in that which one attains by it, but in what one pays for it — what it costs us. I give an example. Liberal institutions cease to be liberal as soon as they are attained: later on, there are no worse and no more thorough injurers of freedom than liberal institutions. One knows, indeed, what their ways bring: they undermine the will to power; they level mountain and valley, and call that morality; they make men small, cowardly, and hedonistic [genüsslich] — every time it is the herd animal that triumphs with them. Liberalism: in other words, herd-animalization...

Letter to the New Orleans Times http://civilwartalk.com/threads/im-a-good-ole-rebel.34939/page-2#post-352510 (8 June 1867)

Introductory
The Grammar of Science (1900)

§ IV
1910s, At the Feet of the Master (1911)
Context: Then as to cruelty. This is of two kinds, intentional and unintentional. Intentional cruelty is purposely to give pain to another living being; and that is the greatest of all sins — the work of a devil rather than a man. You would say that no man could do such a thing; but men have done it often, and are daily doing it now. The inquisitors did it; many religious people did it in the name of their religion. Vivisectors do it; many schoolmasters do it habitually. All these people try to excuse their brutality by saying that it is the custom; but a crime does not cease to be a crime because many commit it. Karma takes no account of custom; and the karma of cruelty is the most terrible of all.