“I dislike Communism because it is undemocratic, and capitalism because it favors exploitation.”

Marxism: Essential Writings, "The State and Revolution"
The State and Revolution (1917)

Source: What is Property? (1840), Ch. V: "Psychological Explanation of the Idea of Justice and Injustice, and the Determination of the Principle of Government and of Right," Part 2: Characteristics of Communism and of Property
Context: Communism is inequality, but not as property is. Property is the exploitation of the weak by the strong. Communism is the exploitation of the strong by the weak. In property, inequality of conditions is the result of force, under whatever name it be disguised: physical and mental force; force of events, chance, fortune; force of accumulated property, &c. In communism, inequality springs from placing mediocrity on a level with excellence. This damaging equation is repellent to the conscience, and causes merit to complain; for, although it may be the duty of the strong to aid the weak, they prefer to do it out of generosity, — they never will endure a comparison. Give them equal opportunities of labor, and equal wages, but never allow their jealousy to be awakened by mutual suspicion of unfaithfulness in the performance of the common task.
Communism is oppression and slavery. Man is very willing to obey the law of duty, serve his country, and oblige his friends; but he wishes to labor when he pleases, where he pleases, and as much as he pleases. He wishes to dispose of his own time, to be governed only by necessity, to choose his friendships, his recreation, and his discipline; to act from judgment, not by command; to sacrifice himself through selfishness, not through servile obligation. Communism is essentially opposed to the free exercise of our faculties, to our noblest desires, to our deepest feelings. Any plan which could be devised for reconciling it with the demands of the individual reason and will would end only in changing the thing while preserving the name. Now, if we are honest truth-seekers, we shall avoid disputes about words.
Thus, communism violates the sovereignty of the conscience, and equality: the first, by restricting spontaneity of mind and heart, and freedom of thought and action; the second, by placing labor and laziness, skill and stupidity, and even vice and virtue on an equality in point of comfort. For the rest, if property is impossible on account of the desire to accumulate, communism would soon become so through the desire to shirk.

Letter to Nathaniel Hawthorne (June 1, 1851).

As quoted in Michael Bakunin (1937) by E.H. Carr, p. 356<!-- New York: NY, Vintage Books -->
Context: I hate Communism because it is the negation of liberty and because humanity is for me unthinkable without liberty. I am not a Communist, because Communism concentrates and swallows up in itself for the benefit of the State all the forces of society, because it inevitably leads to the concentration of property in the hands of the State, whereas I want the abolition of the State, the final eradication of the principle of authority and the patronage proper to the State, which under the pretext of moralizing and civilizing men has hitherto only enslaved, persecuted, exploited and corrupted them. I want to see society and collective or social property organized from below upwards, by way of free association, not from above downwards, by means of any kind of authority whatsoever.

Homo Deus: A Brief History of Tomorrow

Source: Guerrilla Warfare (1961), Ch. I: 5. Warfare on Unfavorable Ground

Le capitalisme, c'est l'exploitation de l'homme par l'homme. Le communisme, c'est le contraire !
[Coluche, Les syndicats et le délégué, Coluche : l’intégrale, 3, Carrère, 1989]
Compare Len Deighton, Funeral in Berlin (1964): "Capitalism is the exploitation of man by man. Yes? Well socialism is exactly the reverse."

Alec and Magnus, pg. 406
The Mortal Instruments, City of Ashes (2008)

Source: How Europe Underdeveloped Africa (1972), p. 134.