In this and other paragraphs, Obama does a good job of breaking down the "two-extremes". Cross explains that most propaganda presents a situation with only two possible approaches or solutions: one right and one wrong, one good and one bad. Obama tries to prevent people from claiming these extremes: that one race is "right", and one "wrong", by addressing the legitimacy of everyone's concerns.

Obama uses plain-folks appeal to relate to his audience on a deeper level. His diverse backstory mimics that of many other Americans.

Obama is stroking the American reader's ego. ("Stroking" a term used by Cross)

I can see Orwell rolling his eyes at this "stale metaphor" which is further weakened by the repetition of the comparative "more". Cross would point out that justice, equality, freedom, and "caring and prosperous" are all glittering generalities.

This nuanced statement has a huge impact on the reader. For one, it sounds good. The alliteration of stain, sin, and slavery catch the ear. It also pairs a biblical allusion of, perhaps, the biggest mistake ever with slavery: the "home of the free"'s deepest historical regret. Obama brings this history to the present with the word "stained", and he shows that the impacts of slavery haven't ended yet. Both Orwell and Cross would approve of this statement's simple language and almost subconscious affect on the reader's thought process.

This is original wording to liven up a common concept. Orwell would approve.