An unpleasant whiff of envy and class warfare surrounds the Margaret Atwood affair. The author found herself on the bottom of a social media pile-on when she spoke out over a proposal to build an eight-storey condo on Davenport Road, near her house. She was called everything from NIMBY to entitled landowner to champagne socialist. Her lawyer told city councillors this week that the attacks on her were "occasionally vile and consistently misrepresentative."

That is unfortunate. The fact that Ms. Atwood is well-known and well-off shouldn't disqualify her from putting an oar in. But the fierce reaction that developed when she and some of her neighbours raised objections to the condo project is, in other ways, highly encouraging. It shows that attitudes about development and density are starting to change. It shows that NIMBY groups can no longer expect to have their way. It shows that Toronto is growing up.

For years, the condo battle has been a tiresome ritual of city life. A developer would propose to build something. The neighbours would erupt in outrage. The local city councillor, afraid of being driven from office, would join in. The building would be cancelled or scaled back.

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Over the past couple of years, the dynamic has begun to change. The neighbours still pack public meetings to rage against the latest development proposal. They still complain about the shadows, the noise, the traffic, the parking problems that they say the new building will inflict on them.

But others – call them YIMBYs (Yes in My Backyard) – are starting to push back. They argue that if Toronto is going to fix its housing problem it needs to build more places for people to live. They point out that hundreds of thousands of newcomers are expected to move to Toronto in the years ahead and that, unless it wants to sprawl to death, the city can't put them all in endless subdivisions. They say that Toronto is going to have to put more housing in the built-up centre of the city. It has to go somewhere and quibbling neighbours can't be allowed to get in the way.

They are right on every point. Embracing urban density is an obvious way to make up for the shortage of affordable housing. It is also a way to build a vibrant city, with more street life, more stores, more things to see and do. The transformation that downtown Toronto has undergone over the past decade is amazing. It comes from all the building, all the new housing, all the new people. We need more of the same.

One reason that Ms. Atwood and friends suffered such blow-back is that, perhaps unfairly, they were seen to be deaf to all this. Don't they know that Toronto has a housing problem, the critics asked? Why would they object to one eight-storey building on a main street, even though city planners had ruled it just fine for the Davenport site?

You can see the first sprouts of the YIMBY movement at those community meetings where people are standing up to say yes to projects in their neighbourhood. You can see it on social media and on comment threads. You can see it among the planners, architects and other professionals who are speaking up in public for a denser city. You can see it in the growing number of people who say they like condo towers, once a Toronto heresy.

Something important is happening here. Politicians had better take notice. The lesson of the Atwood affair is that jumping on the latest NIMBY bandwagon is no longer a safe bet. NIMBY forces have always had the advantage because they were organized. It is easy to rally people to fight a building project that threatens to change their cherished neighbourhood. It is much harder to get people worked up about something as abstract as the need for urban density.

Lately, though, YIMBYs are finding their voice. Some are smart young people with an interest in urban issues. Many have been shut out of the housing market by rising real estate prices. Their self-interest has been engaged, just as it is for the NIMBY crowd. They are still not as well organized, but in time they could become an influential force in city life. Ms. Atwood has started something. We might even thank her for it one day.