When Hollywood takes up a social issue, hard data and clarity can be elusive. My Sister’s Keeper, a drama in theaters this summer, provides a handy example of Tinseltown’s tendency to let tears trump truth.

Told through a series of flashbacks, the plot is set in motion by a medical specialist’s shocking proposal to a mother desperate to save her gravely ill child: Create a genetically engineered sibling who can donate bone marrow and other vital tissue to cheat death.

That suggestion would stop most parents in their tracks. But this mom grabs hold of the idea and runs with it. Fast-forward more than a decade later. The genetically engineered child prompts a family crisis when she refuses to continue her designated role as her sister’s savior.

The setup for this family crisis provides a rich environment for a cinematic meditation on the growing social threat posed by value-free medicine. Instead, the film glides past the utilitarian impulse that sparks the mother’s initial decision. My Sister’s Keeper also ignores the death-dealing that ultimately produces a living child. The camera doesn’t linger in the laboratory, where technicians kill the embryos that fail to provide the ideal genetic match.

The omissions underscore the way our entertainment often distracts us from the grim reality of antilife reproductive technologies and stem-cell research.

While movies frequently address the real and perceived dangers posed by corporate malfeasance, for example, scientific innovation that directly attacks innocent human life rarely provokes outrage.

Indeed, like so many Hollywood dramas that flirt with emerging social issues, My Sister’s Keeper quickly morphs into a celluloid tearjerker. Our emotions are held hostage by the dying patient’s struggle to resolve family conflicts before her untimely demise.

Yet this film adaptation of the best-selling novel by Jodi Picoult also accomplishes something the director probably didn’t intend: Its sentimentality will prompt some viewers to recoil from the emotional arguments that cloud our ability to scrutinize immoral choices.

The film opens with the decision by Anna, the genetically engineered sibling, to seek medical emancipation from her parents. If successful, her move will foil her mom’s plan to keep her older daughter, Kate, alive. Kate’s kidneys have failed, and the doctors want to take one from her healthy younger sister.

As the family absorbs the impact of Anna’s refusal to help her sister, the camera explores the inner thoughts of the mother, whose maternal protectiveness becomes a consuming obsession; the father, whose marriage remains on hold indefinitely; the older brothers, whose pedestrian needs receive scant attention; and the patient herself, an inspiring but doomed adolescent.

Sara, the mother, played by Cameron Diaz, offers the most compelling and honest characterization. Her refusal to surrender her role as the chief advocate for her dying child both inspires and disturbs.

We all know parents like Sara, and a case can be made that value-free science feeds their ferocious pursuit of miracle cures — no matter the cost.

She has made an idol of her child’s survival, sacrificing everything to feed the beast of maternal need.

Yet family members and medical specialists can find no arguments to challenge her stance. Indeed, when Anna finally refuses to donate her kidney, she bases her claim on her right to control her own body.

The film imposes a secular, modern spin on the action, leaving our questions about the characters’ deeper motivations unaddressed. For example, Sara’s husband, Brian, operates in the background, and we never understand the reason for his apparent passivity. He doesn’t question Sara’s initial decision to conceive a “donor” child.

Has he ceded all authority to his wife — or does he share her desperation? If he has qualms about creating a child as a kind of object for use, he doesn’t say so.

Once, the culture understood that children had a right to be born from the loving “one flesh union” of their mother and father. Has Brian forgotten this truth — or did he ever learn it? What kind of moral credibility does such a man possess? None, you might suspect, but the film celebrates his quiet sensitivity and tender moments with his children.

While the tears flow, the characters operate as if they were in the same sterile laboratory environment that facilitated the conception of Anna. Indeed, even Anna, who owes her very existence to the precise genetic requirements of her sister, is a well-adjusted young teen who never rages against her unsought familial obligations.

The character of Anna doesn’t add up: Children care deeply about the origins of their own existence. When a friend of mine told his son that he had been married before and lost his wife to a terminal illness, his son, deeply affected, finally responded, “You mean I might not have been born?” Anna doesn’t seem concerned about such matters.

Of course, there is another more sinister explanation for Anna’s steady equilibrium: Perhaps she has been raised to accept her designated position in the family hierarchy, a position subordinate to her older, and possibly more valued, sibling.

That thought occurred to me as I recalled the plotline of Kazuo Ishiguro’s Never Let Me Go, a haunting brave-new-world novel published in 2005. In Ishiguro’s story about a British boarding school for human clones created and schooled to serve as adult organ donors, the students slowly accept their fate and never rebel. Ishiguro implies that the school’s specially designed pedagogy engenders the students’ passive acceptance of their fate.

Films like My Sister’s Keeper are much less ambitious — or clear-eyed — about the immediate and long-term dangers of scientific hubris that brooks no moral limits. That’s unfortunate, because now, more than ever, we need opportunities for moral reflection. Recently, the National Institutes of Health issued new guidelines that will make it easier for scientists who perform embryo-killing stem-cell research to advance their work.

My Sister’s Keeper allows us to grieve for a dying child and her family. But the tearjerker formula allows viewers to ignore a more important story that Hollywood has no taste for telling.

Joan Frawley Desmond writes from

Chevy Chase, Maryland.