Ugly architecture creates powerful coalitions against development. Sceptics about this have misunderstood how these coalitions work. My latest in Works in Progress: Western countries used to let landowners build almost anything anywhere. Now, strict rules freeze the character of most neighborhoods, banning change and densification. Why? One theory is that modern buildings tend to be ugly, leading residents to support rules that exclude them from their neighborhoods. If this is true, then designing beautiful buildings could lead to more development. Housing reformists have vigorously debated this theory. I do believe that ugliness plays a role in hindering development, but not in quite the way usually proposed. Ugliness is probably not a major driver of opposition to development by local people. Local opponents have many other concerns that are at least as important, like disruption from construction, loss of green space, pressure on local services, and diminished social exclusivity. But there is strong circumstantial evidence that ugliness is sometimes a major driver of opposition among people who live nowhere near the development in question. The first group are often called ‘NIMBYs’, for ‘Not in my backyard’. Let us call the second group ‘NITBYs’, for ‘Not in that backyard’. While a few NITBYs are fervent campaigners, most are only casually interested. Their motives are faint but basically altruistic: their question is whether or not, based on a cursory assessment, a development is an objective improvement to its neighborhood. In certain contexts, the ugliness of a development can summon into being a huge cloud of NITBYs, whose interest in the scheme may indeed be superficial, but who can nonetheless be collectively potent. This model is especially compelling in the case of heritage conservation. Until the 1960s, the redevelopment of historic buildings was almost always permitted; today, it is almost always banned by conservation rules. Supporters of conservationism usually portray it as a response to the destructiveness of postwar planners, while opponents see it as a pretext for suburban NIMBYism. In fact, neither explanation is plausible. On the one hand, postwar planners were no more destructive than the Victorians or Georgians had been: the rate of demolition was historically normal, and cannot explain the wildly unprecedented policy response. And on the other hand, there was no need for NIMBYs to invent pretexts to ban new buildings, as they had already successfully prohibited the kinds of development they disliked in the first half of the century. What had changed, and what generated the host of NITBYs that bore conservationism to victory, was the ascendancy of modernist architecture, a style that is demonstrably far more contentious with the public. Conservationism was a reaction to postwar redevelopment, as its proponents claimed. But it was less a reaction to what the modernists destroyed, than to what they created. This argument can be summarised by the two Paris buildings pictured below. Both were built on the site of older stock, but only one provoked a conservationist backlash. Is this so very mysterious?