Ronald Takaki, in his book A Different Mirror, suggested that one of the reasons for the shift that takes place during the later 17th century in the North American colonies from predominant reliance on indentured servants to chattel slavery was that the indentures were Euro-whites, and therefore could "threaten" the ruling elites with assimilation, while the chattel slaves were Afro-black, which thereby provided a physical demonstration of their separation from the gentry. I don't know if this is, in fact the reason; but the shift during the 1600s from indentures to chattels is certainly clear. As to the treatment of enslaved workers, there were significant differences in the way they were treated depending on the region of colonial North America they occupied and the tasks to which they were assigned. This doesn't mean that anyone in his or her right mind would chose to be a chattel slave, but it is the case that an enslaved worker in Dutch Nieuw Amsterdam or on a small farm in British Colonial New England would have had a very different experience from a tobacco plantation worker in the Virginia Tidewater, a rice plantation worker in the Carolina Low Country, or, in the later US Federal era, a cotton plantation worker in Mississippi or Alabama. There was, in other words, no single, generalized U.S. experience of slavery that can be contrasted, for example, with a generalized experience of slaves in other parts of the New World; not that many authors haven't tried to do exactly this. There's been lots written about all this. A good synthesis is Ira Berlin's award-winning Many Thousands Gone, which traces the history of slavery in the US through its various centuries and regions.