Attempts to free ordinary people from oppression repeatedly led to what Mikhail Gorbachev frankly called "servility" to new despots. How and why are spelled out with both facts and brilliant insights expressed in plain words.
Human nature has been at the heart of the failures of socialism to produce the results it sought, even when socialist leaders were idealists like Julius Nyerere in Tanzania or Pandit Nehru in India.
Nowhere have people been willing to work as well for the common good as they do for their own benefit. Perhaps in some other galaxy there are creatures who would, but the track record of socialism among human beings on earth shows that this is not the place.
Worst of all, the concentration of political power necessary to try to reduce economic inequalities has allowed tyrants like Stalin, Mao and Pol Pot to impose their notions and caprices on millions of others -- draining them economically or slaughtering them en masse or exploiting them sexually.
Mao Zedong, for example, had harems of young girls -- and occasionally boys -- for his pleasure in various parts of China.
There is no point blaming the tragedies of socialism on the flaws or corruption of particular leaders. Any system which allows some people to exercise unbridled power over other people is an open invitation to abuse, whether that system is called slavery or socialism or something else.
Socialism has long sought to create a heaven on earth but an even older philosophy pointed out that the road to hell is paved with good intentions.