Christian G. Appy, in the Boston Globe (May 16, 2004):

ON MAY 4, CNN's Larry King asked Secretary of State Colin Powell about the photographs showing American GIs abusing Iraqi detainees at Abu Ghraib prison. "I don't know what to make of it," Powell said. "I'm shocked. I mean, I was in a unit that was responsible for My Lai. . .. In war these sorts of horrible things happen every now and again, but they're still to be deplored."
It was a startling moment: an unsolicited reference to the most infamous American atrocity of the Vietnam War from a top official in an administration that has routinely rejected any analogies to that failed two-decade-long effort to create a permanent non-Communist South Vietnam. Ordinarily, the Bush administration won't even use the word "guerrilla" - never mind "quagmire" - for fear of conjuring up a nightmarish history. And in the most recent of his rare press conferences, the president insisted that any comparison between our occupation of Iraq and the Vietnam War was not only false but would strengthen the enemy and demoralize our troops.

Perhaps, then, it's a measure of just how rapidly the American mission in Iraq has unraveled that our secretary of state would remind us of March 16, 1968. That was the day a company of US infantrymen landed by helicopter in the South Vietnamese village of My Lai. Though they had been told to expect fierce armed resistance, they did not receive a single round of hostile fire. Nonetheless, during the next four hours, with time out for C-rations and cigarettes, the American soldiers proceeded to slaughter 504 civilians, most of whom were old people, women, and children. According to former door-gunner Larry Colburn, who along with helicopter pilot Hugh Thompson managed to save some of the Vietnamese villagers in My Lai, the GIs "were butchering people. The only thing they didn't do was cook 'em and eat 'em."
As the massacre unfolded, colonels and generals flew in choppers over the scene. Those
officers and many others participated in a massive coverup that successfully prevented the world from learning of the atrocity for 20 months. It might never have surfaced had it not been for the persistence of Ron Ridenhour, a Vietnam veteran who learned of the massacre and reported it to hundreds of military and political authorities. The arrest of Lt. William Calley, a platoon leader at My Lai, did not gain national attention until investigative reporter Seymour Hersh, then working as a freelance journalist, published accounts of the massacre through an alternative news service in the fall of 1969, at first primarily in Europe. Only then did major American publications like Life pick up the story and publish gruesome photographs of the carnage.
The killing of several Iraqi prisoners, and the torture and abuse of others, is not equivalent to the slaughter of 504 Vietnamese civilians. Nor has the military's effort to prevent, or at least delay, the full exposure of wrong-doing at Abu Ghraib equalled the My Lai coverup, which included the reporting of a phony battle in place of the massacre. (The mainstream press, including The New York Times, initially ran the false story, relying on US military accounts.) Yet the two events certainly merit comparison.
Indeed, on the surface some of the parallels are almost uncanny. In both cases GI whistleblowers (Joe Darby now, Ridenhour then) prompted investigation, the work of Seymour Hersh (now writing for The New Yorker) was crucial to public exposure, and graphic photographic evidence made it impossible to refute the horrible nature of the crimes. (As Secretary of Defense Donald Rumsfeld put it in testimony before the Senate last week, "Words don't do it." More significantly, the memory of My Lai should prompt us to think about how the current revelations will affect homefront opinion of the American occupation of Iraq. Then, as now, US officials attributed "un-American" behavior to a few, low-ranking "bad apples" who either lacked proper training or acted in defiance of higher authority. Then, as now, our leaders assured us that the crimes of a few were an isolated aberration from an otherwise just cause. And then, as now, many Americans seemed, for a time at least, willing to believe them.
In 1969 domestic responses to My Lai included a mix of outrage, disbelief, denial, and evasion. Some people insisted that the photographs had been fabricated or that the Viet Cong had actually done the killing. Others tried to diminish the wrongdoing by arguing that the Communists had committed even worse atrocities. With time, however, the "everybody does it" rationale wore thin among a people raised to believe that Americans have a higher regard for human life, and a higher standard of civilized behavior, than their enemies.
Eventually My Lai marked a turning point in American attitudes almost as significant as the Tet Offensive of 1968. Even many who continued to support the war increasingly doubted Washington's ability to prosecute it successfully. And millions who had believed the war a misguided policy or a tragic mistake began to consider the possibility that it was fundamentally unjust and immoral. That claim had long been a staple of speeches at antiwar rallies and articles in underground newspapers, but by the early 1970s it was debated for the first time in small-town coffee shops, executive offices, and mass-circulation magazines.
Not long after My Lai was exposed, antiwar veterans like John Kerry began to testify that war crimes were an inevitable outcome of such military policies as rewarding units that compiled the highest "body counts"; the creation of "free fire zones" in which US forces were permitted to kill "anything that moves"; the burning, napalming, and bombing of Vietnamese villages; the poisoning of wells and food supplies; and the torturing of prisoners with electric shocks from field radios.
Presidential candidate Kerry has downplayed his 1971 claims that US policies sanctioned war crimes. But even now, more than three decades later, evidence continues to surface indicating that the My Lai massacre was exceptional only in its scale of unjustified killing. Last month The Toledo Blade won a Pulitzer Prize for a series of articles documenting a seven-month long "rampage" in 1967 by an elite "Tiger Force" unit of the 101st Airborne Division that included rape, torture, mutilation, and murder. Perhaps the real surprise here is that such stories continue to be regarded as news. Historian Nicholas Turse, writing in The Village Voice earlier this month, reported that he has found hundreds of analogous war crimes in public US military records from the Vietnam War.