Honestly, I'm not sure that's true. In comparing Zinn to Charles Beard, one of the main issues is the simple expanse of time. Sure, Zinn is more acute in the lies he has written, but Beard has had over a century for his poison to become foundational thinking. Here's the thing: Howard Zinn never knew the real America, so his rejection of America is actually easy to comprehend. I reject the lies too, I just go the other way and try to find the truth.
It's Charles Beard's rejection of America, that's the head-scratcher. That's the one that's very difficult to understand. Beard grew up in an era where there were no lies about America - or at least, very few of them. Beard would have been taught the truth about how exemplary of a man George Washington was, it is extremely likely that he read the actual Federalist Papers in school by a teacher who was fond of said papers, and he also would have known of America's early colonial generation and the role that the Church actually played during that time.(not the perverted storylines told today) Beard knew the truth, yet he still rejected America anyways. Talk about radical. Zinn can't hold a candle to that.
I'll put it to you another way. Because of the Beardification of history, that made Zinnification of history possible.
Charles Beard's main claim to fame is that there couldn't have possibly have been any real arguments over Liberty or limited government, no no, that's just school-house fluff and lies.(school houses in his day) The real Founding Fathers were only and solely motivated by money and economics. They were in reality a bunch of greedy SOBs and money grubbers and land-hoarders who had much to gain(in their deep, deep pockets) by agitating for war.
Sound familiar? Zinn doesn't own that storyline. Beard does. And some might even be quick to retort that Beard was discredited. Yes, he was, eventually. But only he was, because his ideal that the Founders were greedy SOBs, that clearly was not discredited. That false narrative has stood the test of time in academia and is alive and well to this very day.
Now it is fair to say that Zinn has expanded that storyline, if not several fold. But let's not grant Zinn all sorts of superhuman powers to which he does not own. His most well known book was published in 1980, compared to 1913 for Beard. From Beard to Zinn, the revisionists between the two, and also let's not forget those who arrived after Zinn and built upon the Zinnified blather is a great example of how progressives "make progress" to new heights.
The real question is, how will the historians be lying about America 40 years from now? Again, just to make sure that the main point is stated twice: Zinn never rejected the real America, because he was never taught it. Beard, on the other hand, rejected the truth outright. The truth is all that existed at the time.
That's truely radical.