Last month it was the cover story in The Atlantic: an explanation of “Why Women Still Can’t Have It All.” Last week came a response from the business pages: “Oh, But You Can.”

Anne-Marie Slaughter, who quit her high-ranking job at the State Department to return to teaching at Princeton University and spend more time with her family, is the author of the magazine cover story. Then Marissa Mayer rocked the male-dominated world of technology when she was named chief executive officer of Yahoo! Inc.— and announced she was pregnant.

The headlines about Mayer are deserved. No one can remember another woman about to deliver a child getting the top job anywhere. Only 4 percent of Fortune 500 CEOs are female, and most of those became so after their child-bearing years were over. The only other tech CEOs, Meg Whitman of Hewlett-Packard Co. and Virginia Rometty of International Business Machines Corp., are 55 and 54, respectively.

In government, too, top jobs — look at the Supreme Court, for example — typically go to women whose children are grown (Justice Ruth Bader Ginsburg) or who don’t have any (Justices Elena Kagan and Sonia Sotomayor).

Back in the Dark Ages, when I was a government lawyer and pregnant, I waited as long as possible to divulge my pregnancy. I preferred to be thought of as fat rather than irrelevant. Who was going to give work to someone who at best would shortly be disappearing for three months and at worst would be distracted for the next 18 years?

So yes, it is good news that Mayer broke the nursery ceiling, especially if it trickles down. Now that we’re done cheering, let’s have a quiet moment to think about who’s more right about the state of women in the workplace: the professor or the CEO?

Slaughter congratulated Mayer on her triumph with the cautionary note that not everyone should try this at home. Mayer, she said, proves her point: The only woman who can have it all is “superhuman, rich and in charge.”

Look at Mayer’s statement about coming back to work. “My maternity leave will be a few weeks long and I’ll work through it,” she told Fortune. Thanks a lot for that.

True, Mayer actually doesn’t need time off in the sense the rest of us do. As the boss, she’s the queen of flextime. Worried about making it to the office for a meeting, or a conference call, or a PowerPoint presentation? Not Mayer. The meeting starts when she says it starts — and will as long as she’s there.

And would Yahoo be giving the job to a pregnant woman if it weren’t already in a what-the-heck state of mind? After all, this is a company whose stock has lost about half its value in the past four-and-a-half years and has scrolled through CEOs like so many instant messages. Mayer’s selection doesn’t mean Exxon Mobil Corp. or International Business Machines Corp. will be picking a pregnant CEO anytime soon.

There’s also a sense that this choice is proof of the “glass cliff” theory, which says a woman only gets a job when the odds are stacked against her success. And when it’s not worth as much anymore. Doors to the medical profession swung open wider for women once it stopped paying so well.

Then there’s money, which is one thing that separates the happy working mothers from the harried working mothers. Mayer, wealthy from her time at Google Inc. and destined to be well-paid at Yahoo, may well change a diaper. But I bet she will never have to run out at midnight to Wal-Mart to buy a box of Pampers. Peek inside the household of a woman at the top, and you will find out that she doesn’t just have a great nanny, she has several. It’s a family version of outsourcing. This doesn’t make Mayer a bad mother — just a more efficient one.

We don’t know, and neither does Mayer, whether her energies and emotions will be divided in ways she isn’t anticipating. The crushing desire to be in two places at once doesn’t end with breastfeeding and frequent visits to the pediatrician.

Slaughter writes about how, once upon a time, she smiled a “faintly superior smile” when another woman told her she would be taking some time off. Slaughter had been part of the chorus “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.” Then she got a job outside academia, working long hours on someone else’s schedule. She quit.

The howls were as loud at this admission as the cheers were long for Mayer. But Slaughter is the one who has the workplace right. It’s a difficult place for working parents of both sexes, although we wouldn’t be having this debate if Yahoo’s new CEO were an expectant father.

This difficulty is not due to a failure of ambition, brains or effort, or of legislation (that said, better maternity leave, flextime and childcare would help). There’s no legislation that will put more than 24 hours in a day or get you home for dinner and bedtime. If you have a child with problems — and who doesn’t at some point? — it’s even harder.

Marissa Mayer, meet Anne-Marie Slaughter. You have a lot to talk about.