Lindsey Clancy's murder of her children is not a "head" problem, it's a "heart" one. 

If every sin can ultimately be explained away by identifying psychological or external influences, eventually nobody is truly guilty of anything. And once guilt disappears, so does the meaning of forgiveness, and so does the need for the gospel. 

Christianity announces sin as our problem, endless excuse-making as rebellion, and Christ as the only hope for wicked sinners like Lindsey, and us.