The director of the Museum of Modern Art on Tuesday night used a forum that was billed as a conversation about the sweeping reconfiguration of its midtown campus to state categorically that the former American Folk Art Museum building will have no place in it.

“We made our decision,” the director, Glenn D. Lowry, told an audience composed of members of the institutions that sponsored the event—the Architectural League, the Municipal Art Society, and the New York chapter of the American Institute of Architects—at the New York Society for Ethical Culture.

The proclamation followed a panel discussion on MoMa’s plans to demolish the 13-year-old former home of the Folk Art Museum as part of a larger redesign of its complex on Manhattan’s West 53rd Street—a move that has drawn the ire of preservationists, architects, and no shortage of rank-and-file New Yorkers.

Elizabeth Diller of Diller Scofidio + Renfro, the architectural firm that MoMa hired to evaluate whether the folk museum could be incorporated into the redesign, also gave a presentation that detailed how she and her colleagues initially believed the building could be salvaged before ultimately concluding that it could not. She cited two reasons for taking up the challenge. “One was we truly believed we could save the building, and we believed that we could breathe new life into it,” she said. “And second was that MoMa’s mission forward was very compelling to us. We’re both supporters and critics of MoMa, and we have some of the same concerns that have been voiced in the media. It’s our museum, too, and we wanted it to be as good as it can be.”

But Diller said she and her colleagues “were unable to find an adaptive-reuse solution” for the Folk Art Museum building, an idiosyncratic structure with a distinctive, 40-foot-wide bronze façade that was designed by the architects Tod Williams and Billie Tsien and completed in 2001. MoMa bought the building in 2011 after the folk museum defaulted on its debts. (Williams and Tsien did not attend the forum.)

One issue, Diller said, was the "vertical organization of the building, with its many stairs and voids" and small gallery spaces. But a bigger problem, she said, is the floor plates in the folk museum building don’t align with the floor heights in MoMa’s existing building. Because the floors support the facade of the folk building, she said, “we came upon this really terrible paradox that in order to save the building, in order for MoMa to have a productive space, it was inevitable that we would lose more and more of the original building and, I would say, its heart and soul.”

Lowry reiterated a point he has made elsewhere—that acquisitions over the past decade, such as the Frank Lloyd Wright archive, have added significantly to the museum’s collection, and to the need for space beyond what was carved out a decade ago in a $858 million redesign by the Japanese architect Yoshio Taniguchi. Lowry dismissed a suggestion from a member of the audience that the museum shift some of its works to its PS1 exhibition space in Long Island City, Queens, as unworkable, calling it a “bifurcation” that would undermine the way MoMa’s visitors experience its collection.

None of this stopped some participants in the panel discussion from taking MoMa to task over its decision to raze the folk museum building. Karen Stein, an architectural consultant and Pritzker Prize juror, was perhaps the most vocal critic, noting that MoMa has a long history of architectural stewardship that dates to its establishment of an architecture department in 1932. “I would expect Walmart to demolish it if they owned it,” she said, referring to the folk building, “but I expect something better from MoMa.”

Two other panelists—Jorge Otero-Pailos, an associate professor at Columbia University’s Graduate School of Architecture, Planning, and Preservation; and the architecture critic Nicolai Ouroussoff—largely limited themselves to theoretical pronouncements. But Cathleen McGuigan, editor in chief of Architectural Record, suggested that MoMa was guilty of a rush to judgment. “It’s got an incredibly important place in our cultural history,” McGuigan said of the folk building. “Alas, it hasn’t had it for very long, and I think that’s why a lot of us are concerned about the speed with which this decision has moved ahead.” Later, she added: “What are we going to think in 10, 15, 25 years when it is gone?”

Stephen Rustow, principal at Museoplan, a design firm that specializes in the presentation of cultural collections, said that whether Diller Scofidio + Renfro had made a compelling case that the folk building could not be salvaged would depend on what its marching orders from MoMa were. “A feasibility study, as all the architects here know, is only as good as the questions that are asked,” he said. “If the question is, find the best, most flexible, optimal use of a particular site … then it’s inevitable that the Folk Art Museum has to be taken down, and I think Liz made that extremely clear.

“If, on the other hand, the question is, we as an institution have decided that there is something of value in the existing pieces of this structure and we want to … find what is best for MoMa while integrating pieces of this history, then I think any number of architects, and certainly DSR, could come back with quite a compelling project that would be very different from the one we see now.”

MoMa’s plans call for replacing the Folk Art Museum building with a new structure that will house spaces for exhibitions and performances. That space also will connect MoMa’s existing building with a planned residential high-rise designed by Jean Nouvel that is to include gallery space for the museum. The plans also call for MoMa’s Abby Aldrich Rockefeller Sculpture Garden to be open to the public from the street during museum hours. Construction is expected to begin in the spring, with completion targeted for 2018 or 2019. MoMa, which is raising private funds to pay for the expansion, has not disclosed an estimated cost.