There's numerous examples where a revolution had a purpose to give more rights to the people but ended up as an authoritarian system when all the power went into the hands of a single person. Some examples are Russia, or rather the Soviet Union with Lenin and Stalin, China with Mao Zedong, Cuba with Fidel Castro, all of which were also leaders with socialist ideologies.
It is a contradiction for sure because the revolutions were led so that the people had more rights, freedom of expression, better life, but ended up giving the power to a single person which did not provided anything of it. Also, if someone tried to oppose the leader usually ended up ''missing''.