More from Agatha Christie’s autobiography. Of course, she doesn’t use the word “sociopath” (or “psychopath” , or “personality disorder”), but I think that is what she is referring to:
Let us face the thought that what we regard as defects were once qualities. Without ruthlessness, without cruelty, without a complete lack of mercy, perhaps man would not have continued to exist; he would have been wiped out quite soon. The evil man nowadays may be the successful man of the past, He was necessary then, but he is not necessary and is a danger now.
(Christie, Agatha; An Autobiography, Collins, 1977, isbn 0-00-0-216012-9 p439 )
There is much she says which I don’t agree with, or is debatable, but she is thought provoking.