"The tenet of radical history that has aged least well is its subordination of analytical problems to political sympathies. The New Left historians were hardly the first cohort of scholars to enlist history in the service of a political crusade or a social agenda. The idea was put forward, in different form, by the Progressive historians of Charles Beard’s time, notably James Harvey Robinson, and many subsequent schools and individuals later embraced it, including some of the... Cold War anti-Communists against whom the New Left historians were rebelling. Conversely, many scholarly-minded radical historians grasped the foolishness, even the danger, of allowing present-day politics to shape one’s readings of past events. It was Christopher Lasch who decried “the worst features of progressive historiography reappear[ing] under the auspices of the new left: drastic simplification of issues; … reading present concerns back into the past; strident partisanship.” Quoting Zinn’s directive for historians to decide “from a particular ethical base what is the action-need of the moment and to concentrate on that aspect of the truth-complex which fulfills that need,” Lasch growled: “In the face of such critics, the consensus historians need no defense.”"
Howard Zinn copied, pasted, and simplified his way to A People's History of the United States. The rest of his scholarship wasn't much better.