According to Bartolomé de Las Casas:
a. Spain needed to institute a more humane system of Native American slavery in order to avoid offending Pope Paul III.
b. converting Native Americans to anything but Catholicism would lead to their death.
c. Spain had caused the deaths of millions of innocent people in the New World.
d. despite his opposition to slavery, he needed to keep his slaves so that he would have time to devote to working for abolition and emancipation.
e. slavery needed to be eliminated entirely from the Earth.