According to Davidson and Lythe, landowners saw the decision between buying a slave and hiring a worker as a pure economic choice, and did not consider the moral issues behind. Hence, they would go for the option that leads to a earning higher profit.
These authors defended that in economic terms, slaves were the smarter choice. Slaves were bought for their whole lives, and even though buying a slave required a higher investment effort in the first moment, afterwards they would provide longlasting labor and value. Also, it was quite improbable that slaves died in the first years and make their owners incur in losses.
On the other hand, hiring workers or servants was cheaper in the short run. Davidson and Lythe supported the fact that these indentured servants had higher probabilities of breaking the terms of their contract. Also hiring workers meant extra taxes that had to be paid by landowners to the colonial authorities. So in the end this option was economically less profitable in the long run.