In an ideal world babies would not be left to cry, but we do not live in an ideal world. Parenting has become increasing isolating and lonely, which is why so many of us SAHM come to the internet for support and advice.
Moms and Dads have to get up for work, grandparents are miles away, siblings, aunts, uncles are not around to help give mom and dad a break, a high needs baby, a baby with other young children, there are many reasons why parents turn to CIO. One big one is the idea that your baby should be sleeping through the night. Once you get over all the shoulds that come with parenting life will be much easier. Baby should be sleeping 5 hours by 3 months, no more night nursing after 9 months. All these rules and suggestions about parenting drive us nuts. Baby needs to sleep in his back, in his own crib, on a hard mattress with nothing, and to top it all off baby needs to learn to fall asleep on his own around 4 months. If not let him cry. To me what is the worst part about all these recommendations is that if your baby doesn't sleep through the night is that you feel like you failed or did something wrong.
This is how I felt during a lot of the first few months with my first.
Liv would only sleep with me, only nurse to sleep. I heard it all, that is dangerous to co-sleep (this is a myth and many studies show that co-sleeping prevents SIDS) that they will never leave your bed, that I am creating a bad habit.
I just have to say that I am lucky that my Aunts and mom did their own thing and nursed us, slept with us and rocked us to sleep. Once I heard that and found attachment parenting I decided to ignore the should of and lead with my heart.
I often saw blogs and post about the physical and emotional dangers of CIO, but most of it was on attachment parenting forums or blogs. I was surprised to see an article about it on WWW.psychologytoday.com a resource I used often in college and several times when I was working on my masters degree in Social Work.
Here is a great article about how crying it and leaving a baby to cry goes against our natural instincts and there is a reason for it.
As I stated about I don't want people who are struggling with a colic or high needs baby to think they are failing or bad. Or just someone who needs to take 5 from a screaming baby, like I admit to having done.
I just want to expose people to other ideas and science other then what the American Pediatrics suggests and almost orders us to do, or according to them, we are not doing our jobs as parents right.
Parenting is not an exact science, but more and more science has been showing us that what we feel in our hearts is most often what is best for your baby.
So feel free and confident to nurse your baby, "spoil" them, hold them tight, kiss them, sleep with them, attend to all their cries, and dote on them and love them as you feel is best.
I always thought I would go with the flow when I had liv. She would sleep when she is tired, we would eat when she is hungry and just live. On demand parenting this is sometimes called and it can work great, for some children. But children crave rhythm an consistence in their life. This is something Liv needed and all my AP books did not offer. She was cranky, fussy and over tired. 
