Built in conjunction with Habitat for Humanity, it is intended not for 26-year-olds with pet-food delivery start-ups but specifically for low-income older people at a moment when the number of adults in Manhattan over 65 and living in poverty is known to have increased by 16 percent during the past decade. Residents of the building will have their own library, computer lab and roof garden.

Beyond that, about a third of the existing garden, which totals about 20,000 square feet, would remain, if absent the eerie romantic beauty that distinguishes it now. The lot was designated for Section 8 housing years ago, but the housing never materialized. Eventually, an outsider artist named Allan Reiver filled it with sculptures from his collection, leasing the land from the city and opening it to the public. It is this notion of the garden as an important cultural asset in a neighborhood whose character has slowly eroded that will be mourned.

But what are the alternatives? Those who would like to keep the garden intact suggest that the building conceived go up across town on an empty lot on Hudson Street. Community activists who oppose development, almost always self-proclaimed progressives in New York, will consistently lead by telling you how committed they are to affordable housing, how important it is to mitigating social inequality and so on. It just so happens that in nearly every case, they have in mind a more suitable location for whatever the city is proposing than the place where they themselves happen to live.

Given that 63,000 New Yorkers are homeless, the city should be building affordable housing on all of its vacant lots, or at least most of them. Lovers of community gardens would resist this idea. They might say that climate change has given the need for more green space a moral urgency, and they would be right. But the city has added more than 3,300 acres of parkland over the past 25 years, and nearly 800 acres just in the past decade.

New York has lost more than 735 units of housing during the past five years because of breakdowns of the community review process. The modern Nimbyist, unlike the 20th-century model, refuses to see himself as a Nimbyist. He is working for the common good. But that common good will never be achieved with the commitment to absolutism that he too often deploys — the blanket rejection of anything new that supplants the old.

Instead, activists could push for buildings that are slightly shorter in the instance of the botanic garden project, for example, or for innovative uses of green space when certain lots are threatened — vertical gardens and living walls, with plant life climbing up buildings, of the kind popularized in other parts of the world. That would look a whole lot more like altruism.