Mother kills her children...evil or delusional compassion

The first time I heard about a mother who had killed her own children and then committed suicide, I was really baffled. How could a mother do such a thing? I believe that her action, as abominable as it was, in her mind was an act of compassion. In her mind, she did not want to abandon her children. She felt that if she could not be there for them, she did not want to risk anyone maltreating them... or having them thrown into foster care. It seems a very unnatural act, but if you can remove any ethical/moral/emotional bias from your judgment, in using cold hard logic (as warped as it may be), you can see how in her own mind (delusional or not) she could do such a thing to her own children. After all, what gives her the right to take away the life of another even if she gave birth to him/her?