Well, revolutionaries are very controversial figures. Still, we got to remember that before Castro there was a Batista, a puppet dictator of the U.S.A. who did quite nasty things. It probably was like it is with a lot of revolutionary groups, at first they start with and fight for noble ideals, but as things get tougher they may need to be more ruthless and pragmatic, or they may actually reach power and be corrupted by it, and in general those groups will lose their north and turn out bad.
I can give specific historical examples for that too, our guerrilla originally was a socialist movement looking to overthrow a very corrupt and uncaring government, to give power to the working class but ended up resorting to extortion, ransom and drug trade to fund itself, as original leaders died and people who cared about war and profit more than lofty ideals joined up. And then, the paramilitary groups were born as farmers tired of getting extorted as the failure government did nothing to stop it, decided to arm themselves and take matters in their own hands, something I'd personally do in their situation. But now they forgot their origins too, and nowadays they extort and kill the same people they originally protected.
About Che Guevara, we'd have to see what his original goals were, more than the end results which tend to go bad in these situations.
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To build may have to be the slow and laborious task of years. To destroy can be the thoughtless act of a single day. - Winston Churchill