My wife is a pediatrician who recently wrote a letter to the Washington Post about this. While she routinely recommends breast feeding, she pointed out that the many costs, or even just personal preference, can justify formula instead. For instance, maternal stress alone probably has a big impact on child welfare. As a result, the weird undercurrent of shame for mothers who don't breastfeed is unwarranted. She sees mothers who are brought to tears because they can't breast feed, when in reality it shouldn't be a big deal, even if it's just a personal choice.