I think it's a thing of majority desire vs. minority acts.
Some people like to see the Empire's practice of slavery as the majority desiring being the faithful conversion of the Minmatar, with some minority indeed doing very bad things to their charges.
Some people like to see the Empire's practice of slavery as a means to abuse and provide a free and easily exploited underclass, with some minority actually intending to care for and uplift their charges.
How you view it decides how you regard things like Breeder slaves and how widespread abuse is.
I, personally, take the former view.
But why does this mean abuse wasn't totally widespread?For me, I see it as a simple logical progression.
If you make someone's life a living hell, they are more inclined to commit acts of disobedience to spite you. They will do this despite the fact that they intellectually realize it will result in punishment - up to and including death - on themselves and possibly any associates as a matter of group punishments. I can present many examples of prisons in which increased harsh treatment lead to increased rates of "acting out", and vice versa - as well as more extreme examples, which I'll leave out for the sake of not turning this into a RL politics argument. The point is, if you don't want to have to be watching over all of your charges every single second of their existence, you don't abuse the hell out of them.
On VitocOne thing that always nags me when Vitoc is brought up is the fact that extended use of Vitoc literally
makes you stupid. No joke.
Studies of Vitoc-Vitoxin interaction in animal brain structures (particularly rats) have also shown a marked diminishing of cognitive function - memory loss and an apparent reduction in basic problem solving skills. These have been tentatively linked to a reduced blood supply in the brain as cranial blood vessels become choked with excess serotonogenic nerve growth.
Okay, so "makes you stupid" is maybe an overstatement, but the point is clear: Vitoc is not a means of control to be used for anyone expecting a slave to be released or "graduate" to a new position. It places inherent limits on a slave's future capabilities even should the immediate need for the Vitoc antidote be removed. Therefore, to me, it doesn't seem like something you'd be dishing out to any and all of your slave population, but merely something you would be giving to the limited numbers who are for various reasons not expected to possibly stand out enough to advance.
EDIT:
Another thought.I think we really need to get a solid definition of "abuse" here.
To borrow the terms Mata defined, the "Mercedes" crowd often argue that a slave is not abused; they do this with the understanding that "abuse" refers to explicit torture, personal damage, rape, etc. They argue that this cannot be the experience of all slaves, because for various reasons that just doesn't make sense - you don't whip your slave for no reason, as it destroys the meaning of the "stick" end of "carrot and stick".
The "Clammy" crowd then argue that even under the least violent Holders, Slaves still have terrible personal living conditions and work under the threat of ill treatment. Thus, they say, the slaves are still abused.
Until we can get a recognition of these two conflicting viewpoints, I don't think a resolution can be found.