I was going to make exactly that point. There are biases in both directions; the author's argument should be that the bias toward harshness dominates.

Also, it's likely that much seemingly frivolous cruelty actually increases the status of its perpetrator. I don't think there's much gain when the victim is so far from you in status as your child, but it's quite believable to me that at least a few million adults are broken enough that it's a possibility.