A very strange book -- strange in the way that only books written a long time ago, or very far away, can be strange. Smith's writing lets us deep inside her mind, into a world where the steady growth of Communism was an existential threat, and where Freudian theories could be spoken without irony or hesitance. I don't know how Smith's story of the South, and her explanation of the region's mindset, is propaganda, but she manages to remain fairly convincing even during her wildest flights of fancy. Much of the pleasure of reading comes from the style, and the rest is, as often happens with these old books, the interest factor of discovering long-forgotten facts and anecdotes (including plenty of bizarre quotes from early-20th-century Southern newspaper editorials).
I don't know enough about the genre to suggest that this is a "classic" of U.S. integrationist literature, but Killers of the Dream does seem to give one of the most powerful accountings you're likely to see about how it felt to be, in those days, a wealthy white woman somewhere between 30 and 50 years ahead of her moral era. Race and money are inherent limiting factors here, as they so often are, but that shouldn't stop you from picking up the book.
As a bonus, my edition contained footnotes from 1961, 12 years after the book had been written, in the midst of the lunch-counter desegregation wars. The notes strike a decidedly more optimistic tone, and make me wonder what similar footnotes might look like, had they been added in 2017. (More confused than anything else, perhaps.)