I had my doubts from the start that breast-feeding would protect my children from everything from Crohn’s disease to cancer, but in the end I breast-fed for a long time. Years. The truth is that it was easy for me, it worked for my family, and I always felt like this time was precious, something I would never be able to do again. But even though I wasn’t breast-feeding primarily for the health benefits, wading into this research was pretty disappointing.

Doctors and researchers generally do agree that breast-feeding reduces the risk of infection, at least during the period a baby is actually breast-feeding. That is certainly not nothing, but here, too, we shouldn’t get carried away. As the director of the Agency for Healthcare Research and Quality explained in 2009, if six babies are breast-fed exclusively for six months, one of them will not get an ear infection she otherwise would have had. That’s about 5,400 hours of breast-feeding to prevent one ear infection. If 26 women breast-feed exclusively for six months, they can collectively prevent one hospitalization for a respiratory tract infection.

So where does all of this moral fervor about breast-feeding come from?

Counterintuitively, for those of us who identify formula manufacturers with big business, the contemporary obsession with breast milk is also driven in part by big business — including the companies that manufacture breast pumps, the companies that make breast-milk-based nutritional supplements, and the companies that sell breast-feeding accessories. The A.C.A. regulation requiring insurance to cover the cost of breast pumps hands breast-pump manufacturers a substantial subsidy. Market analysts predicted that this regulation alone would expand the breast-pump market by more than 50 percent, to almost $1 billion a year in the United States alone, by 2020.

The breast-feeding accessory market, for things like clothes, pillows and nutritional supplements, will be roughly double that. Not surprisingly, some of the research that corroborates the benefits of human milk for infants is funded by companies like Medela, which makes breast pumps, and Prolacta Bioscience, a company that makes infant nutrition supplements from human breast milk. This does not mean that the research is false, but it does mean they have a vested interest in the outcome. It also supports a subtle shift from breast-feeding to the consumption of human milk — a commodity that now routinely trades on the open market.

Most of the intensity surrounding breast-feeding, however, has nothing to do with profits. Breast-feeding has become an important marker of who we are and what we believe in. For some it signals a commitment to attachment parenting, for others it is an environmental issue, and for still others it is a protest against the predatory marketing practices of the big formula companies. Some parents on the Christian right see breast-feeding as a sign of the rightness of heterosexual marriage, with different roles for men and women, and some feminists believe it is an emblem of female empowerment and the life-sustaining force of female bodies.

Recently, breast-feeding advocacy has begun to generate a backlash as some women, including some feminists, chafe against the message that women who don’t breast-feed are bad mothers. We all want to protect our children from every danger that we can, but some experts believe that up to 15 percent of women don’t produce enough milk to feed their babies. And it’s a lot easier to comply with the recommendation to breast-feed exclusively for six months if you are a stay-at-home mom with a breadwinning partner. In a country where the average working mother who goes on maternity leave returns to work 10 weeks after having a baby (and nearly 30 percent of new mothers take no maternity leave at all), breast-feeding for any length of time is very hard to do.

The effect of the moral fervor surrounding breast-feeding goes beyond mere shaming. It also reflects, and reinforces, the divisions of race and class that have long characterized American social life. Although 91 percent of women in the top income quintile breast-feed, 71 percent of those below the poverty line initiate breast-feeding. Whereas 81 percent of white women breast-feed, 62 percent of black women do. Breast-feeding is a lifestyle choice the majority now make, but it is more common among white middle- and upper-middle-class parents.