"You are pitiful isolated individuals; you are bankrupts, your role is played out. Go where you belong from now on - into the rubbish-can of history!" - Leon Trotsky, to Martov and his Menshevik followers, after the October Revolution
Kind of him to warn them.

They walked away anyway.
Some of my favorites:
Somebody says: "Of no school I am part,
Never to living master lost my heart,
Nor any more can I be said
To have learned anything from the dead."
That statement - subject to appeal -
Means "I'm a self-made imbecile."
Goethe, Den Originalen
"Eternal vigilance is the price of liberty—power is ever stealing from the many to the few…. The hand entrusted with power becomes … the necessary enemy of the people. Only by continual oversight can the democrat in office be prevented from hardening into a despot: only by unintermitted Agitation can a people be kept sufficiently awake to principle not to let liberty be smothered in material prosperity."
Wendell Phillips
[too bad that people tend to quote only the first seven words]
"With each slain being an entire world dies. For that reason arithmetic provides no measure for ethics. Irreversible evil cannot be measured."
Stanislaw Lem
"I divide my officers into four classes; the clever, the lazy, the industrious, and the stupid. Most often two of these qualities come together. The officers who are clever and industrious are fitted for the highest staff appointments. Those who are stupid and lazy make up around 90% of every army in the world, and they can be used for routine work. The man who is clever and lazy however is for the very highest command; he has the temperament and nerves to deal with all situations. But whoever is stupid and industrious is a menace and must be removed immediately!"
Kurt von Hammerstein-Equord
"Terrorism is the war of the poor, and war is the terrorism of the rich."
Peter Ustinov
"We don't know who 'discovered' water, but we can be pretty sure it wasn't a fish".
Marshall McLuhan
"The optimist proclaims that we live in the best of all possible worlds; and the pessimist fears this is true."
James Branch Cabell
"De tous les systèmes economiques et sociaux, le capitalisme est sans conteste le plus naturel. Ceci suffit déjà à indiquer qu'il devra être le pire."
Michel Houellebecq (thanks, kronic, the guy wrote some interesting books)
"The worship of will is the negation of will. . . If Mr. Bernard Shaw comes up to me and says, «Will something,» that is tantamount to saying, «I do not mind what you will,» and that is tantamount to saying, «I have no will in the matter.» You cannot admire will in general, because the essence of will is that it is particular."
G. K. Chesterton
"The Government are very keen on amassing statistics - they collect them, add them, raise them to the nth power, take the cube root and prepare wonderful diagrams. But what you must never forget is that every one of these figures comes in the first place from the village watchman, who just puts down what he damn pleases."
Unknown british civil servant, about British India
"In life everything has either a price or a dignity."
Kant
"The modern conservative is engaged in one of man's oldest exercises in moral philosophy - that is, the search for a superior moral justification for selfishness"
J. K. Galbraith
"I would rather be vaguely right than precisely wrong."
J. M. Keynes
and finally one again current after a century:
"I am more concerned with the return of my money than the return on my money"
Mark Twain