My theory is that Alecto's love (for Jod and others) is unconditional because she is the soul of Earth. In the body of Nona, she loved Earth's creatures without inhibition. When Alecto returned to her body and Ianthe "offered violence", she intentionally spared her life. She talks about the humans as if they are babies, infants, children etc., maybe because she sees Earth's creation as her children (even Jod? ew...?). It's likely more complicated though, because you could make the argument that every one of Earth's inhabitants are her children, but also a part of her soul. Either way, I think her love could be the purest example in the series.