Hard to know if they are hypothetical people....but, I think it has to do with varying degrees of what they do. If it is a super parent dominant house where the kids are spanked or threatened with spanking throughout the day (as I have sadly seen), I would never leave my kids there. If they do CIO starting as a newborn and never go to the kiddo, even when sick, etc - again, I'd never leave my kids there.
But, there are families that I, for the most part, really like. They may not make all the same choices as I do, but I think they are overall great families. I can think of one friend who did rarely give her kids a spanking - one swat on the bottom. I don't think it is the best parenting strategy, and I have never done it, but it is far from beating a kid. I have another friend who did resort to CIO after a year and a half of sleep deprivation. Again, I don't think it is the greatest choice, but at that point, I think she did what she had to do. If my kids were overall really comfortable with these people, I think the risk of emotional trauma from one swat on the bottom once a year is less than the risk of being transplanted and left with people a kid doesn't know and having to form new bonds with them, even if they are really gentle people. But, again, hard to know unless you have real people with real examples of behavior! Glad you don't have to really make that choice!