It's ambiguous because Prospero is not ever punished for his actions. However, Montaigne's "Of Cannibals" is all about cultural relativity and argues that the peoples Europeans encounter on their voyages are not savage or barbarous but instead are more civilized in many ways than Europeans. Shakespeare's use of that speech, and Gonzalo's sympathy for what he thinks are the indigenous people of the island suggest that Shakespeare was at least sympathetic to that idea.