These people are forgeting that Batista was a bad man and needed to be ousted. Even the US government would not allow him to live in the US after he fled Cuba.
And Castro didn't come out of the closet and reveal himself as a full-blown communist until he was successful in ousting Batista and taking over the country.
Not hard to believe that a leftist revolutionary would hide his true ideology until he was in power - isn't that exactly how Barack Obama did it?