I guess my own position is tainted by the belief that slavery is fundamentally wrong as a restriction of freedom, not as a matter of being beaten. So if I were a slave, though I would personally prefer not to be beaten, I would also prefer slavery be seen as a vile practice, and if I have to take a few beatings to make that be known, I would take them.
The alternate of nobody being beaten, but still being slaves where everybody is waffling and unsure about whether slavery is bad because nobody is being beaten seems to me a bit like a losing proposition. It's the same reason we can't do effective political reform today: people will choose their own convenience when they're not facing a visible evil as a group.
The last thing I would want is for people to think I got beaten because I'm a "naughty slave" or because my owner was a particularly bad guy. No, the reason I got beaten was because I couldn't choose my path. Because I was a slave, and slaves can't choose not to be beaten, even if they would prefer it. When a slave gets beaten, he or she is beaten by slavery as an institution, not by some violent individual.
How much different would the world be if Hitler had announced from day 1 his play to conquer Europe and massacre millions of people? Heck, if we had ended slavery 100 years earlier, maybe we'd be 100 years closer to managing global warming. We don't have time for evils to fester in the margins pretending to be nice.
I remember a couple years ago there was some politician saying we don't need minimum wage laws because companies already pay more than that, so the law is redundant. And in the name of "small government" declared that we should remove the law from the books. All because his favorite corporations are "nice slaveowners" who don't beat their slaves, he thinks that there's nothing wrong with destroying a very important institutional protection.