Open this photo in gallery Mayoral candidate Sarah Climenhaga speaks to the media following a live debate at Corus Quay in Toronto on Sept. 25, 2018. Tijana Martin/The Globe and Mail

“The city is creating gated communities, closed off to low-income people.”

That’s Sarah Climenhaga, the progressive candidate for mayor, and those fiery words capture what could be the most important idea in this Toronto election: that public policy is making inequality and the housing crisis worse.

Ms. Climenhaga is picking up on an argument that’s been floated by progressive local planners and also by the Toronto Region Board of Trade: that Toronto is preventing “gentle density,” killing the construction of housing units in the service of so-called neighbourhood character.

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We should be listening.

“People say, ‘Where are we going to put all this housing?’” Ms. Climenhaga says rhetorically. “Well, we have tons of room to put housing if in our neighbourhoods, instead of single-family houses, we have duplex, triplex and small apartment buildings.”

That sounds simple. And it is. Toronto is a very big place, and most of the city is covered by single-family homes. These zones have relatively few people, and their population is largely shrinking.

These “neighbourhood” areas have been nicknamed “the Yellowbelt,” by the planner Gil Meslin, in an analogy to the Greenbelt that provincial policy has placed around the city. The city’s official plan commits to preserving “stable residential neighbourhoods,” but they’re not stable. The houses stay the same, or get replaced by monster homes. But these places are housing fewer people.

Why not fix all this by loosening up some planning rules, and letting some apartments be built? Because that’s politically toxic. Affluent homeowners hate it. “There’s an incentive to not rock the boat with the small group of people who vote in this city,” Ms. Climenhaga says. “Residents are just afraid of change in their neighbourhood. And instead of challenging that in an open way, the temptation for politicians is to defer.”

And they are. At the recent Board of Trade/Globe and Mail mayoral debate, both John Tory and Jennifer Keesmaat sidestepped the question. Instead, Ms. Keesmaat cited her worthy, but challenging, plan to build 100,000 subsidized homes over a decade. Mr. Tory, meanwhile, boasted about the alleged success of the city’s tiny and flawed Open Door Policy. Which has, in in its best year, approved – not built – about 1,200 partly affordable homes.

But this is a city of 2.8 million, and more than 90 per cent of us live in market housing. Which is why some progressives see so much importance in zoning reform.

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It’s also an issue about which the more you learn, the more the conventional wisdom starts to look dishonest and classist. Almost every neighbourhood in the city already has some mix of rental and owned housing. But anti-development arguments are usually made by house people, who try and pretend those apartments don’t exist.

I spoke recently with two planners, Blair Scorgie of the firm SvN and Sean Hertel, who have been concerned about this issue. “It’s enormous for Toronto,” Mr. Hertel says. “We are effectively sterilizing growth across much of the city.” He points out that the old city of Toronto has a smaller population now, around 650,000, than it did 50 years ago.

And the social and economic consequences are broad: School closings. Failing neighbourhood retail. A lack of private investment. Seniors aging in place with nowhere to move. “I think people may not understand the issue,” Mr. Hertel says, “but they see the symptoms.”

Mr. Scorgie and Mr. Hertel, who also teach at the University of Waterloo, have some solutions in mind. Mr. Scorgie proposes “density transition zones,” effectively stretching the development corridors known as “avenues,” on streets such as Eglinton, into the blocks on either side. This is a fine start.

But first, the two agree, Toronto needs to start by rethinking its approach. “Our official plan and zoning are creating unrealistic expectations about what a neighbourhood should be,” Mr. Scorgie says. “Cities change.”

In Vancouver, this issue is prominent in the current municipal election. Pro-development YIMBY (Yes In My Back Yard) arguments are prominent: Mayoral candidate Hector Bremner is arguing to “legalize housing.”

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In Toronto, that sort of thing still sounds odd. But Ms. Climenhaga is hoping we can get this conversation going before Toronto reaches Vancouver’s insane heights of unaffordability.

“Right now, there’s intense development in a few areas,” Ms. Climenhaga says, “and then the rest is completely private and unaffordable. That’s a completely inequitable situation. Even if all we care about is equity, we’d have to change that.” She’s right, and our leaders need to start the work.