A basic human tendency is to consider other people as being rational. Disagreeable perhaps but rational nonetheless. Except for those who commit such unspeakable acts as the Utah father, Michael Haight, who recently killed his mother-in-law, his wife, and their five children ranging in age from four-years through seventeen-years. This occurred two weeks after his wife filed for divorce. He had earlier removed guns from the house apparently so his victims couldn't defend against his planned attack.
Two-years before his oldest daughter, Macie, then fourteen, reported to the police her father's multiple assaults and the extreme abuse she suffered which made her, to quote a news article, "very afraid that he was going to keep her from breathing and kill her." Which he did.
This raised the significant question of why nothing was done by the police. The possible answer, that the wife refused to press charges, isn't sufficient since Macie had clearly been harmed. Had an adult behaved similarly toward another adult they would have been jailed (hopefully, though this is not certain in these odd times). Yet the testimony of youth even older than Macie tends not to taken as seriously as an adult's.
Another possible answer for why children aren't removed from an abusive family is the belief that children are best raised by biological parents despite aberrant parental behavior. This, even in states where judicial decisions are required to be "in the best interests of the child," is hardly ever done. Only rarely are parental rights abrogated with children being freed for adoption.
Not that foster care is always better: a recent news item descirbed foster parents who not only sexually abused their two young wards but prostituted them.
Clearly, more sophisticated evaluations are needed of both criminals and foster parents, and greater education of police and judges too in the hope that, finally, decisions are made consistent with the safety of children rather than hoary philosophy.