When Rod Serling created the science-fiction suspense series The Twilight Zone in 1959, he did so partly as a way to smuggle stories of social injustice (particularly racism) under the cover of metaphor. Even he could not have wished for better outlines than the ones contained in two of this year's Oscar nominees for best picture. An African American wakes to find his rights and identity have vanished. A homophobic cowboy discovers he has Aids, and is subjected to a helping of his own foul-tasting medicine from those who assume him to be gay.

Both 12 Years a Slave and Dallas Buyers Club are worthy of an audience's time and admiration but they each play variations on the same calculating game. In using an outsider figure as a way in to downbeat (or unsexy) subject matter, they illuminate their own idiosyncrasies and surprisingly little else. Solomon Northup is not your run-of-the-mill slave: born a free man in upstate New York, he is an accomplished violinist who is shown blithely shopping for finery. Nor is Ron Woodroof, in Dallas Buyers Club, a typical sufferer from the early days of Aids. He has contracted the disease through unprotected heterosexual sex. His virulent homophobia is noteworthy not because it should have had prophylactic properties, but because it scores the film valuable irony points.

That homophobia provides an access route for any viewers who might otherwise have been frightened by the idea of a movie about Aids or gay men. Yes, Dallas Buyers Club is so good that even homophobes can enjoy it. Which raises the question: does a filmmaker really want to be chasing an audience at any cost? Commercially the tactic is understandable. Artistically, I'm not sure there isn't a small price to pay.

It's chastening to realise that Ron's homophobia (real or imagined, that is: some of those who knew him claim he was neither bigoted nor exclusively straight) will provide comfort for anyone resistant to such a subject. Dallas Buyers Club is a clever movie but some of its cleverness is expended on insisting that Ron is not to be feared – which contrasts him pointedly with a transgender Aids patient (played by Jared Leto) in much the same way that flamboyantly gay characters are inserted into buddy movies to dispel any suspicions about the heroes' sexuality (Withnail and I springs to mind).

12 Years a Slave and Dallas Buyers Club would not have been greenlit if they had told the stories instead of an untalented African American born into slavery or a gay man who contracted Aids. But there is a downside to novelty. I can't have been the only person watching 12 Years a Slave who felt that Northup somehow merited his fate less than the other slaves shown on screen. After all, he was born out of chains; he is talented and literate (the film is based on his memoir). How unfair that he of all people ended up beaten and humiliated.

In that instant, the film has worked its invidious magic. Suddenly we find ourselves differentiating between those who are deserving of slavery and those who aren't. The same impulse was at the heart of the film adaptation of John Boyne's (fictional) novel The Boy in the Striped Pyjamas. That movie's distressing climax shows Bruno, the young son of a concentration camp commandant, trapped inside a gas chamber with hundreds of Jewish prisoners. I shed copious tears during the ending, but none of them were for the millions of Jews who perished in the camps. My tears were for Bruno. Poor Bruno. He should never have been in the gas chamber. He should never have died. The others were meant to be there. That was their fate. Not his.

These are not reactions to be proud of. But it's important to acknowledge that even the most conscientious film can place the audience in a cleft stick. 12 Years a Slave and Dallas Buyers Club are adhering to the same storytelling process by which a news report on war focuses on a single unusual victim rather than evoking the deaths or suffering of thousands of others. The tragic and the upsetting usually aren't enough to earn a place in the headlines. Give us the oddities and ironies of a human interest story every time. Our feeble brains often can't grasp any more than that.

12 Years a Slave is out now. Dallas Buyers Club is released 7 February