Why do people take on the burden of fostering a child, only to abuse them?

This woman had two men in her life that sexually assaulted the children in her care, and she seemed complicit (and an accomplice) to these crimes. To me, I focus on her and not the men, because she was not only an adoptions supervisor, but had taken in dozens of other children. You would think the mothering instinct could overpower whatever a boyfriend or husband might say or do. Yet, here she is... admitting she had a rape-murder fantasy, and helped hack up a body that was killed months before.

People are sick, and this woman takes first place. I hope her family ignores her, and no one speaks to her for the rest of her life.