Interestingly, the modern idea of a historical "flat earth" was actually created by atheists:

No one before the 1830s believed that medieval people thought that the earth was flat. The idea was established, almost contemporaneously, by a Frenchman and an American, between whom I have not been able to establish a connection.... But now, why did the false accounts of Letronne and Irving become melded and then, as early as the 1860s, begin to be served up in schools and in schoolbooks as the solemn truth?

The answer is that the falsehood about the spherical earth became a colorful and unforgettable part of a larger falsehood: the falsehood of the eternal war between science (good) and religion (bad) throughout Western history. This vast web of falsehood was invented and propagated by the influential historian John Draper (1811-1882) and many prestigious followers, such as Andrew Dickson White (1832-1918), the president of Cornell University, who made sure that the false account was perpetrated in texts, encyclopedias, and even allegedly serious scholarship, down to the present day. A lively current version of the lie can be found in Daniel Boorstin's The Discoverers, found in any bookshop or library.

Can you imagine them carrying out such a campaign, knowing full well it was false? The struggle against god-belief is well worth a few (thousand) such compromises, surely.

At the time of Cornell's founding, White announced that it would be "an asylum for Science — where truth shall be sought for truth's sake, not stretched or cut exactly to fit Revealed Religion"

Beautiful words, no? Truth sought for truth's sake. While systematically publishing historical accounts and scientific myths he knew to be fictional. Just another strand in the great snarled tapestry bequeathed to us by those who valued truth far more than their opponents. Countless people believed this for over a century, and many still do today. Well, all for a good cause.

Atheism shouts that it will wield truth against its opposition, but the historical and geopolitical record suggests that deception and coercion have been far more effective.