and I think that flashback is to signify that Schultz finally starts to actually "get it,"--what the whole slavery thing is about, how terrible it is, and that by buying Broomhilda back, even if that means the mission is a success, that he is upholding slavery and the horrors that come with it. In realizing this, he decides that he can't live with himself, so he kills Candie, knowing it means he'll die to.
Basically, he makes the transition from being guilty white liberal whose motives are to distance himself from the "bad" whites, to actually being down for the cause and willing to fight and die for it. I've personally seen, in real life, white liberals experience a great deal of cognitive dissonance as they have gone from speaking out against white supremacy to actually understanding it and realizing that they have benefitted from it and in many ways upheld it. The shift in moral compass is often frightening for them, which is why they are so adamant in NOT talking about issues or telling us to "get over it." They don't wanna talk about it or face it cuz it fukks with their entire self-concept of being a "good" person as they realize how much they benefit by living in a white supremacist society.
The more I think about this movie, the more I believe it is designed to throw the curtains back on white supremacy and is a harsh critique of it. It seems to say, "hey, this is what white people think of you, and this is how they justify it, and it's all STUPID!" or from a white person's perspective, "this is what we think of them and how we treat them, we have been irrational and childish (hence Candie and Candie Land), and it's STUPID because they show more humanity than we do (all the white characters, except Schultz, are actually subhuman and lacking insight/character/intelligence, while all the black characters, even the uncle tom, show insight and humanity). This movie is asking everybody to wake up.
What I'm surprised not too many people have commented on in this thread is how black people are portrayed in this flick and the commentaries made on contemporary black issues--how we think of ourselves and how we are scared of "them" on a psychological level...I think the ending is basically saying that we have no need to be scared, we don't need white people to save us, that we can do it on our own...just that we've been conditioned otherwise.
I swear that song is on repeat in my head since I watched the OG version back in November.
" after he shot Candie. 
