NIMBYISM IS AT LEAST as old as the suburbs, but it’s a shape-shifting impulse. Over the years the objects of its wrath have evolved, particularly in affluent areas, to include not just undesirable neighbors (landfills, prisons) but also what many people would consider desirable ones, such as chic stores and modern transit hubs. The idea is the same and deeply conservative: Don’t change our neighborhood! Don’t build it here!

That sentiment, among others, is behind the virulent opposition to a pair of major projects now at a critical juncture in the approval process: the second, $2.8 billion phase of Metro’s Silver Line extension to Dulles International Airport and points west; and a $250 million proposal to build a shopping, residential, office and hotel complex near College Park, all anchored by what would be the first Whole Foods supermarket in Prince George’s County.

The Silver Line is a much-delayed venture that would furnish the Washington area with a basic amenity — transit access to its main international airport — that is taken for granted in most affluent world capitals. Nonetheless, it is at risk of major delay, and possibly collapse, because of opposition in Loudoun County, where freshmen Republican members of the Board of Supervisors and some constituents are balking. Among their complaints is that bringing Metro into the county would cost too much and transform what remains mainly a bedroom suburb into something much more dynamic.

“I don’t want 40,000 new jobs in Loudoun, and slowing growth by 10 percent or more would be a blessing,” Bill Knecht, a Sterling resident, wrote to us in a letter to the editor last month. “Think what we could do with the millions we save by not pouring it into Metro.”

Mr. Knecht is understandably concerned that the face of his community would be drastically changed by the construction of a nearby Metro station. But we disagree with the assumption that Loudoun would be better off without Metro, let alone wealthier by “saving” the money.

As has been proved in Arlington, Bethesda and elsewhere, Metro brings employment, jobs and high-salaried professionals — exactly the kind of development that produces enormous revenue for local governments. By contrast, single-family houses, which tend to be filled with school-age kids, cost localities more than they generate in tax revenue.

For Loudoun, killing off Metro while continuing to build housing subdivisions is a big-time, long-term money loser. It would undercut the county’s economic competitiveness, leading businesses to locate elsewhere while saddling county homeowners with the disproportionate burden of paying for schools and other services. The result: Taxes on homeowners would soar, traffic would mount and commutes would get longer.

With or without Metro, Loudoun is changing. With Metro, the change will be more manageable and more affordable.

THE PARTICULARS OF the debate in Prince George’s are different — Metro is already there, and the Purple Line, a new transit link, is probably coming — but the flavor is similar. A reputable developer has proposed the sort of project that Prince George’s needs — an upscale mini-town center whose centerpiece, the Whole Foods, would be packed with shoppers on Day One of the target opening, in January 2015. As with Loudoun, Prince George’s desperately needs to develop an economic and commercial tax base that will ease the fiscal burdens on a county that has grown too reliant on soaking homeowners.

Despite that, some local residents — a vocal minority in a community that does not lack for skilled advocates — are fighting to block it. They complain that the project would worsen traffic, which is true, and that its location is ill-suited to the leafy neighborhoods it would abut.

As in Loudoun, the opposition is understandable; it’s also misguided. The Cafritz Company, which has owned the land for decades, is proposing the right kind of project for an inside-the-Beltway parcel surrounded by affluent communities. It has enlisted Whole Foods, a symbolic feather in the cap for a county that has complained for years that it is spurned and bypassed by high-end brands who prefer whiter, wealthier suburbs.

In epic negotiations with local planning officials, Cafritz has committed to a long list of measures that would ease the traffic, environmental and noise impacts, provide quick access to a nearby Metro station and enhance the project’s design. If there are aspects of the project that still rankle neighbors — for instance, if 1,000 housing units is too many — they will remain open to negotiation in subsequent stages of approval.

For now, though, Cafritz is seeking a rezoning that would allow the project to go forward to the next stage. The Prince George’s County Council should accept the recommendation of the county’s planning staff and approve it.

The Cafritz development, like the Silver Line, will indeed change surrounding neighborhoods. But neither Loudoun nor Prince George’s will have much success by imagining that it can close the gates, ignore the region’s ongoing growth and exclude the kinds of amenities, along with the people who use them, that are in demand elsewhere. In the long term, that’s a recipe for failure.