If you really want to see a heated debate, don’t bother with politics. Find a “mommy blog” and look for a thread or post on working moms vs. stay-at-home moms. You can almost be guaranteed that the comments will be filled with some of the most vicious vitriol you’ve ever seen.

Ever since women started to enter the workforce in large numbers seeking careers, as opposed to simply working because they had to as in earlier times, the debate over whether or not women can balance family and a career has been raging.

A while back in The Atlantic, Anne-Marie Slaughter came clean. She was the first woman director of policy planning at the State Department and before that she was a law professor and then the dean of Princeton’s Woodrow Wilson School of Public and International Affairs. She describes herself as a committed feminist:

“All my life, I’d been on the other side of this exchange. I’d been the woman smiling the faintly superior smile while another woman told me she had decided to take some time out or pursue a less competitive career track so that she could spend more time with her family. I’d been the woman congratulating herself on her unswerving commitment to the feminist cause, chatting smugly with her dwindling number of college or law-school friends who had reached and maintained their place on the highest rungs of their profession. I’d been the one telling young women at my lectures that you can have it all and do it all, regardless of what field you are in. Which means I’d been part, albeit unwittingly, of making millions of women feel that they are to blame if they cannot manage to rise up the ladder as fast as men and also have a family and an active home life (and be thin and beautiful to boot).”

Knowing that, Slaughter’s epiphany is all the more moving, especially given the family struggles in the background. She continues:

“In short, the minute I found myself in a job that is typical for the vast majority of working women (and men), working long hours on someone else’s schedule, I could no longer be both the parent and the professional I wanted to be—at least not with a child experiencing a rocky adolescence. I realized what should have perhaps been obvious: having it all, at least for me, depended almost entirely on what type of job I had. The flip side is the harder truth: having it all was not possible in many types of jobs, including high government office—at least not for very long.”

What is fascinating is how much she highlights the existing social pressures on young women, particularly by older feminists, to eschew family for a professional career.

“Yet the decision to step down from a position of power—to value family over professional advancement, even for a time—is directly at odds with the prevailing social pressures on career professionals in the United States. One phrase says it all about current attitudes toward work and family, particularly among elites. In Washington, ‘leaving to spend time with your family’ is a euphemism for being fired.

Only recently have I begun to appreciate the extent to which many young professional women feel under assault by women my age and older. After I gave a recent speech in New York, several women in their late 60s or early 70s came up to tell me how glad and proud they were to see me speaking as a foreign-policy expert. A couple of them went on, however, to contrast my career with the path being traveled by ‘younger women today.’ One expressed dismay that many younger women ‘are just not willing to get out there and do it.’ Said another, unaware of the circumstances of my recent job change: ‘They think they have to choose between having a career and having a family.’

A similar assumption underlies Facebook Chief Operating Officer Sheryl Sandberg’s widely publicized 2011 commencement speech at Barnard, and her earlier TED talk, in which she lamented the dismally small number of women at the top and advised young women not to ‘leave before you leave.’ When a woman starts thinking about having children, Sandberg said, ‘she doesn’t raise her hand anymore … She starts leaning back.’ Although couched in terms of encouragement, Sandberg’s exhortation contains more than a note of reproach. We who have made it to the top, or are striving to get there, are essentially saying to the women in the generation behind us: ‘What’s the matter with you?’

They have an answer that we don’t want to hear. After the speech I gave in New York, I went to dinner with a group of 30-somethings. I sat across from two vibrant women, one of whom worked at the UN and the other at a big New York law firm. As nearly always happens in these situations, they soon began asking me about work-life balance. When I told them I was writing this article, the lawyer said, ‘I look for role models and can’t find any.’ She said the women in her firm who had become partners and taken on management positions had made tremendous sacrifices, ‘many of which they don’t even seem to realize … They take two years off when their kids are young but then work like crazy to get back on track professionally, which means that they see their kids when they are toddlers but not teenagers, or really barely at all.’ Her friend nodded, mentioning the top professional women she knew, all of whom essentially relied on round-the-clock nannies. Both were very clear that they did not want that life, but could not figure out how to combine professional success and satisfaction with a real commitment to family.”

It isn’t easy to break out of society’s expectations, especially for young women. But what if those expectations go against our natural, biological inclinations?

Women, of course, are the ones who carry the child through pregnancy and have the biological capacity to nurse. It also follows that throughout history and in very different cultures, women have generally been more nurturing and focused on child-rearing than men. Fathers play a part too, but it is often quite different. Perhaps traditional roles have existed not because they are societal constructs, but because they are biological inclinations.

That’s a tough pill to swallow in this day and age. Yet, it may do more to explain the internal struggle of women trying to balance family and a career than most anything else. Anne-Marie Slaughter is probably right, you can’t have it all.