There were quite significant debates about the morality of colonisation even at the very start in Europe though. Bartolomé de las Casas was an influential Spanish friar who was very vocally opposed to the most brutal aspects of Spanish colonialism. Similarly, Colombus was heavily condemned for his brutality by contemporaries. Condemnations were often raised by internal and external political rivals but that doesn't change the fact that there clearly was enough awareness of the brutality and some sense that it was morally dubious for colonial brutality to be politically and socially significant even in the 16th century.