The issue - the decision whether or not to buy someone - always came down to economics, to be cold.
Ignoring the moral and ethical arguments against slavery - there is an expense to keeping a person as a resource - feeding, housing, clothing, and maintenance of health - and the investment to purchase someone with the understanding that very few would take that person off your books once that slave is no able to provide you with a revenue source actually reduces the value of that investment over a long period of time.
The economics of keeping slaves - vice keeping indentured servants or hiring someone - is only an optimal method of maintaining labor if the requirements for the owner is such that a slave can be kept working in some capacity for the financial benefit of the owner until close to the time the slave will die.
Small farmers did not need slaves. It is less expensive to hire several people or buy someone's bond for the seasonal field or occasional repair work than keep a slave that you don't also need to help you in the day to day of maintaining a small house.
Hire someone - they went home after you didn't need them. Buy someone's bond - you'd only have to worry about the cost/benefit ratio of keeping them for a couple years while they were still in the peak of their strength, and then you let them go off and didn't have to think about them ever again.
Businesses that were not based at a residence site - including mining - also did not need slaves. Businesses need laborers only in the peak of mental and physical prowess - maybe they'd need some duffer as a watchstander or a stable hand after work hours if they didn't have shift workers that would also clean up the site and act as security as part of their work. And that's about all they would need for labor.
The expense of just the minimal keep for a person or a group of people from effectively the age of 10 until the day they died far outweighs the cost of hiring someone for the five to twenty years and not also having to provide that person with enough food, board, and medical for their lifetimes.
The only situations in which possibly use and maintain a slave force were the large plantations, wealthy people's homes, or some form of 24 hour inn or hotel where if the slave couldn't do physical labor, there was always the light household work (mending, "minding", serving, light cleaning, prep work) and the housing and food requirements for the slave could be leveraged off the amount of resources and waste hosting businesses or large residence facilities naturally required or produced.
The thing to remember is that under the law, slaves weren't considered the same as livestock, even during Colonial times. You couldn't just kill them without cause when they became too old, weak, or expensive to keep.
While the laws found in any of the Colonies - no matter if it was Dutch, English, French, or Spanish - didn't care if you worked or punished someone to death, they did uniformly require that if you owned a person, you were responsible for feeding, clothing, housing, and otherwise maintaining that person until either the bond was paid off, or you could sell him/her - or that person died of "natural causes" (which included punishment for infractions that could withstand an inquest if you lost too many bondsmen/women or slaves).
Plantation owners and hostel-owners were recorded as facing severe fines or potentially jail time if they were have found to have personally tortured or killed slaves and/or bondsmen/women out of hand - mainly because of the fear of slave uprisings that could possibly be viewed "justifiable" self-protection by any reasonable person. Overseers typically were blamed for any legally defined mistreatment, and were promptly fired and/or charged in most cases where the slave owner should have been charged with gross neglect, assault, torture or murder.
Disclosure: At least one of my ancestors came over as an indentured servant in the late 1600's (and promptly ran away, settling in the mountains of North Carolina and built up a successful farm and smithy that allowed him to pay off not only his bond, but those of a few other run-aways who settled with him) and another had escaped from Missouri and was able to "pass" enough in the 1850's to re-invent himself and become a senior partner in a successful insurance business in Chicago in the 1870's.
I learned quite a bit about the legalities and economics of owning people in the Americas when looking at the background environment of their lives a decade or so back when I was doing a genealogy.
Haele
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