"It is notorious that the news of the Emancipation Proclamati..." — Christopher Hitchens quote meaning

It is notorious that the news of the Emancipation Proclamation was kept from the people of Texas and not celebrated until 'Juneteenth'. There may be those in Texas now who believe they can insulate their state—a state that had its own courageous revolution—from the news of evolution and from the writing in 1786 of a Constitution that refuses to mention religion except when demarcating and limiting its role in the public square. But we promise them today that they will join their fore-runners in the flat-earth community, and in the mad clerical clique of those who believed that the sun revolved around the earth. Yes, they will be in schoolbooks—as a joke on the epic scale of William Jennings Bryan. We shall be fair, and take care to ensure that their tale is told.