It isn't so much the beatings that make 12 Years A Slave hard to watch-- they will, in any case, not appall the moviegoers who have made the Saw and Hostel franchises profitable, and there are only a few of them-- it's the endless pitilessness of the white characters' attitudes toward the black characters, their utter inability to recognize them as human beings.
Paul Giamatti and Benedict Cumberbatch are miles apart morally, but notice how each feels about separating families at the auction block. Even those who on occasion rescue protagonist Chiwetel Ejiofor show little concern for him as a human being afterward.
The society of 12 Years A Slave is similar to the one in Django Unchained, but is far more detailed and without any sympathetic characters, except perhaps Brad Pitt, who, as an Amish man, is a bit of an outsider.
Even the slaves themselves for some reason seem distant from each other. You expect some kind of love story, but there isn't much, and even the hero, as the story goes along, loses what hope and initiative he began with until he is practically the numb animal the whites assume him to be. And this is apparently a true story taking place before the Civil War. There is no anticipation of better times ahead.
But it's a brilliant piece of moviemaking. All the acting is first-rate, and I haven't even mentioned Michael Fassbender, Paul Dano, Sarah Paulson and Alfre Woodard.
The concentration on relations between slaves and whites is so unrelenting that it may account for the neglect of relations between slaves and slaves.
And don't neglect to read the notes with the closing credits. 12 Years A Slave isn't quite over even when it's over.