“Although these indentured servants were only temporary slaves, they were slaves in every sense of the word.“
As long as sense of the word dies not mean being born into slavery and being a slave until the moment you die.
Considering that the average lifespan was about 35 and the living conditions of the indentured a 15 or 20 year indenturment would be for life in most cases. The indentured were much cheaper (the cost of passage) than slaves who were resistant to the rampant malaria and were therefore treated worse because of the ease of replacement.