I do not know what Columbus said but if he did say something like that it is probably not representative of his thought which, in turn, is not representative of the attitude of the Spanish government. Columbus was a great navigator but a very bad leader and ruler of men. In spite of that he wrote letters to the King and Queen where he advised limiting the licenses for gold searching and encouraging people to settle the land and implement the customs and government system of Spain. His view and that of the Spanish government was to encourage settlement and commerce and to convert the Indians.
It is very PC these days to paint all Europeans as bloodthirsty, wealth-stealing oppressors of the natives but in this case it is just not so. It is a fact that the Spanish monarchy always considered itself to be the protector of the Indians and never condoned enslaving them and always considered them free people to be converted to Christianity. Obviously there were abuses but they were always against official policy and they were denounced by Las Casas and other authors.
The Spanish monarchy considered the Indians as newly acquired subjects just like any other it had acquired in Europe. Spain assimilated the conquest of America to the conquest of any other European land and respected the usages of war at that time and tried to respect all legal formalities. The fact that it was breached many times does not detract from the fact that it was the officially mandated policy.
In the conquered territories the native rulers and princes were recognised as nobility so long as they submitted to the Spanish Crown. Spanish soldiers in Tenochtitlan (Mexico) were given orders to show the Mexican chief Montezuma the respect due to a noble prince and some were punished for not abiding by this.
All in all, In the 16th century, Spain was very much ahead of her time when it came to awareness of what today we would call human and civil rights. The Emperor Charles commissioned a group of theologists, moralists, etc to advise him on the rights of the Indians and how they should be governed. Orders were always given that the laws and customs of war should be observed and legality was always very much a concern in the conquest and settlement of the Americas.
In the 16th century there was nothing in Europe comparable to the “industrial” slave plantations which would evolve later in North America. Spain and Portugal had a long history of fighting Muslims and both sides would enslave each other’s prisoners and generally hold them for ransom. The profit was in selling them back more than anything else.
After about 1750 slavery changed drastically, especially in the New World. As slavery evolved over the centuries into more of a commodity trade it was acceptable to buy slaves from other countries in Africa because they were buying people who were already slaves. The Spanish Monarchy considered itself to be the protector of all its subjects and that included the American Indians but the Spanish monarchy did not consider itself protector of the African slaves any more than the American government today considers itself to be the protector of citizens of other countries.
Anyway, my post refers exclusively to the Spanish colonies and not to the part of North America settled by the Anglos.