Well, history is effectively written by the victors, so it will be written so that the ends will retroactively justify the means, or at the very least will be scrutinized far enough into the future that we can disengage emotionally.
If Castro's dream was to avoid Cuba from turning into a Haiti or a Honduras, it was a resounding success. If it was about turning it into a socialist utopia where people lived as if was the first world, it would probably be unrealistic in the first place but things remain to be seen.
The point is that, in fact, we do justify evil when it aligns with our policies and goals, because a lot of our well-being depends on it. The American quality of life depends a great deal on the intervention and installment of puppet regimes in countries that provide natural resources to guarantee a steady stream of supplies for manufacture; that was the basis of the Monroe Doctrine and it justifies atrocities to a level where Castro's worst was just baby play.
I actually do agree that there is evil in the repression of the country, but at the same time good is not the absence of evil either, and you can't talk about the evil without recognizing the successes of the Cuban regime. Otherwise you cannot even begin to make a single claim on the good things of the US because it has been based, to a great degree, on the control and oppression if millions of innocent people through projected global power.
No dude, "evil" is a social and cultural construct. We are doing this as a species, as in relying on taboos and moral rules, in order to survive. It's why we don't fuck our relatives, kill our children or eat our dead. This inherited culture is how 7 billion of us live on this earth without killing each other. And we need it because frankly many of us are too stupid to be rational all the time.
As for calling "evil" when seeing it, this is basically about communicating to other human beings a danger sign that can be universally understood. Which is in itself an act that can be used for evil, like the US propaganda for entering Irak, but then again we are flawed creatures trying to live our lives.
What I'm trying to say here is that this isn't an argument that you can win. And I'm not even sure that being more rational would be good for us. Because IMO even perfectly rational people can be easily fooled into believing flawed statistics and logical fallacies and I don't even care what Fidel's dream was for Cuba because the end never justifies the means IMO.