Sam2, yes he enslaved the native people on some islands (despite the queen’s distaste for slavery, if you can believe some web page I found). That’s hardly the same as enslaving a continent. He wasn’t the first or the last conqueror to enslave the conquered people (think of the Bnai Yisrael in Canaan). Slavery involving Africans was also nothing new.
Europeans were obsessed with gold, so regardless of which European would have been first to reach the New World, bad stuff would have happened.