In discussions such as this it is difficult to point out the 'other side' w/o sounding like you are defending the indefensiable. But slavery was a fact at the time. There are a couple of things that can be pointed out:
A stong high quality slave was an expensive asset from the perspective of the slave owner. As such a smart business man used those assets wisely in order to maximize his return in his investment. I would suspect that the treatment of slaves was in many cases proportional to their cost to the owner and this owners business acumen.
When a slave owner had particularly dangerous tasks that needed to be done, rather then risk a costly asset, he would sub contract this task out to others, who were less valuable then his own slaves. Much of this type of work fell to new immigrants, many of which were Irish, at this time.
Re: "A stong high quality slave was an expensive asset from the perspective of the slave owner. As such a smart business man used those assets wisely in order to maximize his return in his investment."
An interesting point, one I used to use myself but there is a flaw. Not everyone is a smart business man. By this logic there would never be reckless driving of expensive automobiles nor would there be poorly maintained vehicles. There will always be stupid people but with slavery it was a human being that would pay for the neglect. Still more slaves were left alone more than we commonly think.