Perhaps the best retort to Buchanan is Ellison:
Whitman viewed the spoken idiom of Negro Americans as a source for a native grand opera. Its flexibility, its musicality, its rhythms, freewheeling diction and metaphors, as projected in Negro American folklore, were absorbed by the creators of our great 19th century literature even when the majority of blacks were still enslaved. Mark Twain celebrated it in the prose of Huckleberry Finn; without the presence of blacks, the book could not have been written. No Huck and Jim, no American novel as we know it. For not only is the black man a co-creator of the language that Mark Twain raised to the level of literary eloquence, but Jim's condition as American and Huck's commitment to freedom are at the moral center of the novel.
In other words, had there been no blacks, certain creative tensions arising from the cross-purposes of whites and blacks would also not have existed. Not only would there have been no Faulkner; there would have been no Stephen Crane, who found certain basic themes of his writing in the Civil War. Thus, also, there would have been no Hemingway, who took Crane as a source and guide.
Without the presence of Negro American style, our jokes, our tall tales, even our sports would be lacking in the sudden turns, the shocks, the swift changes of pace (all jazz-shaped) that serve to remind us that the world is ever unexplored, and that while a complete mastery of life is mere illusion, the real secret of the game is to make life swing. It is its ability to articulate this tragic-comic attitude toward life that explains much of the mysterious power and attractiveness of that quality of Negro American style known as "soul." An expression of American diversity within unity, of blackness with whiteness, soul announces the presence of a creative struggle against the realities of existence.
Without the presence of blacks, our political history would have been otherwise.
No slave economy, no Civil War; no violent destruction of the Reconstruction; no K.K.K. and no Jim Crow system. And without the disenfranchisement of black Americans and the manipulation of racial fears and prejudices, the disproportionate impact of white Southern politicians upon our domestic and foreign policies would have been impossible. Indeed, it is almost impossible to conceive of what our political system would have become without the snarl of forces—cultural, racial, religious—that makes our nation what it is today.
Absent, too, would be the need for that tragic knowledge which we try ceaselessly to evade: that the true subject of democracy is not simply material well-being but the extension of the democratic process in the direction of perfecting itself. And that the most obvious test and clue to that perfection is the inclusion—not assimilation—of the black man.
I just came across Saul Bellow's 1952 review of "The Invisible Man." Check it out.