crying

This rant is regarding letting babies "cry it out". Why, I ask, why? A story, for example:
This morning, one of my colleagues was talking about her baby girl who didn't sleep through the night until she was 10 months. Much earlier, mom let her "cry it out", while mom went down to the basement in order not to hear her little girl screaming in distress. Obviously, this baby was not ready to sleep through the night and was letting her mom know it.
Why, and how, could you ignore your baby's painful, distressed calls for you? I truly believe that we are part and parcel of the animal kingdom, and it is written in our DNA to respond to our young, to protect them and keep them safe from predators, real or imagined. My son can whimper from across the house and something in me hears him even when the sound in barely audible, and I run to him to scoop him up, to protect him and let him know that he is safe. I will protect him from the bears and the lions and the crows, from the dangers of the night and the dangers of all that is unknown to him. He knows me, and he trusts me, and I will never betray that most tender of bonds between us. I am his mother, his protectress.