They committed a genocide on an entire region because they refused to follow state-approved clergy and join conscription. If I remember right, about 200,000 people died. Also the main ideological forefather, Jean Rousseau, was apparently a disgusting human being who abused his wife and neglected his children all while claiming society is oppressive and shackling him down for dare criticizing his grotesque behavior. The word sadism literally came from one of the French Revolutionaries, De Sade who believed true freedom meant being as sexually depraved as possible. The worst communist dictator in world history, Pol Pot, was less inspired by Orthodox Marxism, and more by Kropotkin and especially the French Revolution (He was educated in leftist French circles), especially figures like Babeuf.
The French Revolution was evil, so is socialism and communism.
"In Italy, comrades, in Italy there was but a Socialist able enough to lead the people through a revolutionary path, Benito Mussolini"
~Vladimir Lenin