A reply to /u/MattyMumbles

It will be good if you list what "actions" you are specifically asking about. The approach and conduct of conquistadors varied widely over time and over different locations. There was little argument against Spain's right to conquer those lands. But there were many arguments on how the natives should be treated, and what rights they had.

Perhaps you can read through an old post on Las Casas' advocacy of native American rights and some earlier debates in Christianity.

In the early parts of exploration, the coming of missionaries almost always lagged behind the arrival of explorers and conquistadors. Spain sent administrators and missionaries as part of their mission to spread Christianity and also to better control her agents. You see the same pattern time and time again, from Columbus to Cortés and Pizarro. At the level of the royalty of Spain, they tended to take an idealistic view of how things should be, but gave in to pragmatic limits of their influence and competing objectives almost everywhere. This includes control of territories, the need to generate revenue, and the need to encourage further exploration and colonization.