BY INTIMIDATION and the veiled or open threat of violence, a motley band of white supremacists, Confederate sympathizers and self-appointed advocates of Southern heritage are endeavoring to halt the city of New Orleans’s efforts to relocate monuments lionizing the Confederacy. By impeding the lawful, legitimate acts of an elected government, the statues’ champions, some of them bearing weapons, are not merely disturbing the peace; they are also revealing their contempt for the basic values of a multicultural democracy and a highly diverse city. They cannot be allowed to succeed.

New Orleans’s plan to remove the four monuments was put in motion by a 6-to-1 vote of the City Council in December 2015, a few months after Dylann Roof, a white supremacist enamored of Confederate symbols, massacred nine African Americans at a prayer service in Charleston, S.C. “The time surely comes when [justice] must and will be heard,” Mitch Landrieu, the city’s Democratic mayor, said at the time. “The Confederacy, you see, was on the wrong side of history and humanity.”

Mr. Landrieu has been patient and cautious; now, having beaten back frivolous legal challenges to the city’s plan, he deserves support. His intent is not to destroy the monuments, as obstructionists falsely portray it, but to relocate them to a museum, garden or other site suitable for historical artifacts. That is fair treatment for the monuments, which date from the late 19th century — statues of Confederate President Jefferson Davis, Gens. Robert E. Lee and P.G.T. Beauregard, and a 15,000-pound obelisk, nearly 40 feet tall, commemorating the bloody 1874 attack by a racist white militia on integrated police forces during Reconstruction. (The obelisk was removed last month.)

In the flux and reinvention of many big American cities, much goes under the bulldozer’s blade; no one is suggesting that fate for these monuments, which, especially in the case of the Lee statue, are resonant for many New Orleanians. However, it is a historical fact that the Confederacy rose up against the United States in order to preserve an economic system based on slavery — an affront to fundamental human rights. The Confederate cause and its icons, overtaken by history, are now deeply offensive to many Americans, including black people, who happen to make up a sizable majority of New Orleans’s population.

In a local newspaper, the Advocate, an indignant white New Orleanian, Frank B. Stewart Jr., disingenuously likened the relocation of the monuments to the destruction of the Egyptians pyramids or the Roman Colosseum. That’s nonsense; the monuments will remain in New Orleans, accessible to the public. Relocating the statues would memorialize and contextualize a distant time without dishonoring it.

In the meantime, Mr. Landrieu and New Orleans authorities need and deserve help from the FBI and other federal law enforcement agencies to ensure that the open threats by fringe figures — some of whom stand vigil at the statues fully armed, as permitted by Louisiana’s open-carry law — are not fulfilled. The statues’ removal must not be impeded by violent extremists.