In Chapter 1, Du Bois explores the false promise of freedom used to lure Black Americans into accepting a kind of half-citizenship in the decades following the Civil War. Ironically, as Du Bois notes,
Few men ever worshiped Freedom with half such unquestioning faith as did the American Negro for two centuries. . . . To him so far as he thought and dreamed, slavery was indeed the sum of all villainies, the cause of all sorrow, the root of all prejudice.
This statement from Du Bois utilizes irony to highlight the fact that enslaved Black Americans worshiped freedom and the American Dream as near apostates, despite not yet having access to that freedom themselves. Naturally, this points to the American Dream being founded upon a mythic, idealistic, aspirational equality that the Founding Fathers themselves—many of whom owned enslaved people—failed to fully uphold.
Once freed from the institution of chattel slavery, however, Black Americans soon saw that their idealistic vision had perhaps been a little too reliant on the good graces and magnanimity of their oppressors. Slavery could be abolished, but the prejudice remained. By introducing irony in this passage from Chapter 1, Du Bois sets the reader up to empathize with the deep disappointment felt by Black Americans who so exalted U.S. notions of freedom but never received those same freedoms.