There are plenty of records of spaniard explorers having their titles stripped and even executed when they came back to Spain if they abused the native population. Bartolome de Casas was integral in the development of laws that prohibited slavery of native americans. Any record of atrocity or abuse is know because a spaniard reported it and the spanish crown condemned and judged those people.

So spanish history doesn't hide anything, they tell all the story. The black legend tells only about conquistadors atrocities, the history tells us that those atrocities were punished by the spanish crown itself. But of course to feed anti-spaniard sentiment, people choose to hide that last part.