For an allegory, killing a serial killer in self defense (but before he actually kills you, gasp) does not make you a serial killer.
While this is a true statement it does not follow that preventive actions against people who hold fascist views, but do not act on them, is anyway different what the Nazis did to people.
So why don’t you believe any of the other leaders believed in socialism?
The USSR Politburo only cared about itself. Same with the CCP and the Kim family. These are extractive institutions that are only self serving. They are not beholden to anyone so they have no incentive to care what the people want.
Also this is great man theory taken to an extreme.
He didn’t get the right to lead from inherently being a great man. He got it by leading his people in a revolution against a dictator. His policies benefited enough people so they continued support him. Castro actions were based on his personal moral compass. The fact Cuba didn’t become like North Korea is great. If Cubans aren’t giving meaningful mechanisms for dissent going forward, they will have little recourse to prevent their government from becoming like the Kim regime.