They are mourning him because he was on "their" side. For the political left it doesn't matter how many murders are committed, how much misery is bestowed upon a population, how much naked hypocrisy, no matter how many families are ruined and torn apart and bereaved, none of that matters as long as the goal is the pursuit leftist-socialist-utopia.
"Communism is an evil thing, folks. It is an ugly, evil, vile, inhumane thing, and Castro was one of the world's most dominant communists ever."
"It's a great myth that communism is about upward mobility for the bourgeois, for the middle class, for the proletariat, for the hoi polloi. That's a big myth. Communism, socialism is all a scam designed to keep people impoverished. Better to control them. It's designed to enrich the leaders. It's an oppressive, tyrannical form of human arrangement. And the lie is that it is the only way lower middle-class people can have upward mobility. It's just absolute BS."
"All this equality and sameness and equal rights and fairness, you go to any communist country, there's none of that. And there never will be any of that. There's never any of that in liberal societies. There's always anger and misery and unhappiness because it's a false promise that a bunch of dupes end up believing, and it never happens. The leftists succeed in blaming capitalists for the failure of Marxism, socialism, communism. It is just despicable."
"The fact that this way of governance has not been dispatched forever is one of the enduring mysteries to me. The explanation obviously is psychological, and I intend to discover it. I intend to find out what it is. To me it's unacceptable that people still find anything redeemable in it, even hope, because there is clearly none of that."
This will never change.
As my father often reminds me "there will always be a new crop".