Movies on difficult-to-solve race issues are always hard to fathom

The director knew he was treading a delicate political correctness minefield today with a race-based movie like this. It's even becoming more difficult to discuss historical race issues like this because in 2014 there's so much new race-based (or race-baiting) taboos about depicting the ugliness of racial bigotry and racism in all its horrendous glamour way back when.

Political correctness is the new fascism of our age; Hitler, Stalin, and Mao would have been delighted to see their ultimate victory over the West in the 21st century.

All that said, I'm like you OPs here. What is this movie really trying to convey despite its clearly overt historical plot of a mulatto girl facing polite upper society's skin color bigotry in the 18th century. Is this supposed to be the 18th century version of Rosa Parks?

Some other OPs asked more intriguing questions, some of which stirred up a hornets nest with the race baiters who go epileptic apoplectic anytime someone discusses race.

What if the actress was played by the more beautiful Paula Patton or Beyonce?
You're all too old to remember these actresses but what if the character was
played by Jayne Kennedy, beautiful in her 70s prime, or,
I'd say to the above questions, no difference. It would not have been about the beautiful face, but the darker skin.
Okay, what about this curveball?
What if the mixed race woman looked mostly white or could pass for white, as in the archaic terms, quadroon, and octoroon?
Settle down, now trolls; I'm just referring to those, yes, bigoted terms that were actually used in history. I didn't make them up myself.
Well, if the movie's character was a quadroon or octoroon, it would pretty much derail the plot line's real plotline, that of an historical event that would lead to Britain abolishing slavery in due course. You would be left with a different plotline, one in which slavery does not come up as an issue but a more mundane one of keeping the girl's minor part-black heritage a secret and if her lover can accept her hidden African heritage and will love conquer all? To that question I'd say we're talking then about a totally different movie and to really answer that, no, love often doesn't conquer all because well into the mid-20th century and even later, there was still talk about white people hiding their African genes even though they looke as white Caucasian as can be.
So we end up with at least another controversial movie about historical race which might satisfy those critics who have a race agenda, turn-off those critics who don't like themes like this used to turn a dollar at the cinema, and then the general public who may or may not quite understand what they're getting into by attending this movie. It may be neither fish nor fowl in attempting to be both.