Fidel Castro stands in a long line of great socialist leaders who betrayed socialism. The list pretty well includes all of them, from Lenin, Trotsky and Stalin, to Mao Zedong and Chou En-lai, to Pol Pot and the Khmer Rouge in Cambodia, to Mengistu in Ethiopia.
In the name of the beloved masses, these revolutionaries became the greatest mass murderers in history, responsible for genocide, famine, incalculable suffering, widespread torture and the deaths of tens of millions of workers for the crime of somehow displeasing their great leader.
Castro was not a mass murderer of the same order, though hundreds, maybe thousands, of opponents were executed in the early years. He also broke the hearts of the millions of Cubans who welcomed his revolution.