Of course the language and violence in 12 Years a Slave makes you wince, but the brutality here is as sleek as a knitting needle, and slips between your ribs to get at you somewhere deep, beyond simple expressions of disgust or disbelief. McQueen has no intention of turning his film into a Western liberal guilt-trip — he doesn’t have to. What we see speaks for itself. 



Although the explicit swear words used in this movie may seem awful to you, nothing will compare to the sheer punishment inflicted upon the slaves, it is almost as if someone is trying to get you to fully understand how much hatred was dished out upon these people until you are slightly in disbelief   by the contents of the film. McQueen doesn't want this film to be a typical slavery film by putting a specific view by villianizing the slavers. The story itself will automatically depict who was right and who was wrong.

http://www.telegraph.co.uk/films/2016/06/03/12-years-a-slave-review-this-at-last-really-is-history-written-w/