Why do you think Crusoe was unhappy when he was a slave?

Slavery is a common theme in Robinson Crusoe. Crusoe himself becomes a slave owner, owning a sugar plantation in Brazil which relies on slave labor for its cultivation. Earlier in the story, Crusoe's ship is attacked by Moorish pirates. Crusoe is captured and made a slave by the pirate captain. He's not exactly thrilled at the prospect. After all, he must have some idea as to how degrading and miserable the life of a slave can be. But then Crusoe is treated quite well by his captors, performing mainly light duties aboard ship. He certainly isn't forced to experience the kind of back-breaking toil of a slave in a sugar plantation.
Yet Crusoe still yearns to be free. As a white European, he probably feels that slavery is something that should only happen to the so-called lesser races. It's shameful and undignified for a member of a privileged race to be reduced to the status of a slave. In order to regain that privileged status, then, it's necessary for Crusoe to escape. After two years of servitude, that is precisely what he does with the help of Xury, a young boy. Once they are rescued, Crusoe actually sells Xury as a slave to a Portuguese captain, who helps him to purchase a sugar plantation in Brazil. Whatever Crusoe may have felt about his own captivity, it's patently obvious that he has no moral qualms about the institution of slavery itself.