I disagree with this - I believe letting a baby cry CAN do a lot of damage to a baby's sense of self-worth. A baby cannot understand why you will respond to its cries sometimes, and at other times ignore them! Crying is the only way a baby can communicate. If you ignore this communication then the baby has nothing. A baby who is left to cry and stops crying after a while does so, not because he is suddenly happy again, but because he has lost faith in his ability to communicate with you. Leaving a baby to cry it's eyes out does not feel right for the baby, and does not feel right for the mother. So why do it?!
Also, I believe that a baby cannot be 'held spoiled'. That is a very old fashioned idea. Baby's NEED to be held a lot. It is natural for them to feel insecure when alone, as prior to birth they have never been without physical contact with the mother. Just as they have had constant physical contact before birth, so they should after. I carry my 3 month old around all the time as it is the best way to keep her happy. I did the same for my 2 year old, who now feels so safe and secure, is very happy, and independant - not clingy at all - bacause she got the physical contact she needed when very young. Limiting physical contact and letting a baby cry CAUSES clinginess and insecurities later on.

This is only my opinion, personal research and experience. It is just one method of parenting ('attatchment parenting') and I know different methods work for different parents. I do not wish to offend anyone!