On the end note: yes, and they died, if Harmony had made that same sacrifice, his own death as penance, then it would have been less bad.
In this case slavery is: the obliteration of a persons will, either by threat of pain/death to self or others, or as Harmony does, literal removal of that will. I used the example of torture because it was during a debate on that issue, and some common theoretical situations used to justify it, that I came to this conclusion. In this case slavery is worse than death because it directly makes a free willed sentient nothing more than an object, a tool of anothers will, and they then can be used to do further harm, this is worse than a killing because, while death is terrible and an evil in and of itself, it does not make the target a tool, they remain themselves even if only in death, a slave looses that.