What in the world has happened to Jason Reitman? After a quartet of excellent films—“Thank You for Smoking,” “Juno,” “Up in the Air” and “Young Adult”—he’s stumbled twice in succession, first with the decidedly labored romantic melodrama “Labor Day” and now with a ponderously didactic ensemble piece. “Men, Women & Children” is so determined to deliver a message about setting aside messaging devices and connecting with one another in person again that it doesn’t bother to create credible characters, situations or dialogue. One would like to think that it’s intended as satire, or at least a comedy; but it offers no evidence of that, remaining glum and glibly monitory throughout.

Like “Disconnect,” Henry-Alex Rubin’s similarly themed (and structured) film of last year, Reitman’s—adapted by him and Erin Cressida Wilson from a novel by Chad Kultgen and set in Austin, Texas—offers a collection of interlocking plot threads. One centers on a married couple, Don (Adam Sandler) and Helen (Rosemarie DeWitt), both of whom are unhappy and reach out via the Internet for a kind of companionship. He masturbates over porn, while she clicks onto a dating site, eventually linking up with an unnamed but receptive Dennis Haysbert. Meanwhile their fifteen-year old son Chris (Travis Tope) has become so addicted to Internet sex that he’s unable to react to real-life encounters, even when his sultry classmate Hannah (Olivia Crocicchia) comes on to him; he’s happy to exchange suggestive texts with her, but when it comes to performing in bed, he can’t.

Hannah is a high-school cheerleader who aims, with the help of her supportive mother Donna (Judy Greer), to develop an acting career by posting revealing photos on a website. Donna may consider the Internet her friend, but that’s certainly not the attitude of Patricia Beltmeyer (Jennifer Garner), the epitome of maternal protectiveness, who monitors all sites visited, as well as calls or texts received or sent, by her daughter Brandy (Kaitlyn Dever). Brandy, a bright, sensitive girl, attracts the eye of handsome Tim (Ansel Elgort), who’s been so emotionally devastated by the departure of his mother for a new life—and marriage—in California that he’s left the school football team on which he was an all-star and does little anymore but play an Internet interactive game called Guild Wars. That worries his father Kent (Dean Norris), who’s so concerned about the boy that he attends Patricia’s parents group where he meets Donna, and they strike up a relationship that quickly takes a turn toward more than simple friendship. Tim and Brandy, meanwhile, start what must be—in light of Patricia’s obsessive surveillance—a clandestine teen romance. A final plot thread involves one of their classmates, anorexic Allison (Elena Kampouris) , who visits sites about how to get even thinner and becomes so besotted with another football hunk that she goes to bed with him, with predictable results that shock her parents (J.K. Simmons and Tina Parker).

Allison’s is only one of the parallel stories that take such a dark turn. Even more elaborate is that of Brandy and Tim, who’s devastated again when Kent limits his Internet access and Patricia simultaneously intervenes to break off his relationship with her daughter. That interference nearly causes a tragedy. On the other hand, Donna comes to realize how detrimental to her daughter’s future the website they’ve been employing can be, and her decision to close it down ruptures her relationship with Hannah. Inevitably, Don and Helen eventually find out about each other’s real and virtual infidelity, leaving them to consider whether they can continue their life together. Their son’s problems are apparently left unresolved.

Reitman and editor Dana E. Glauberman follow the twists and turns of all these narratives pretty clearly, never missing a chance to emphasize the theme of the alienation caused when people become so tied to their devices that they’re no longer able to communicate with their fellow human beings other directly. But just in case you don’t get the message, the picture adds a woebegone framing device in which shots of the Voyager spacecraft hurtling through space are accompanied by arch observations spoken by Emma Thompson, who points out how insignificant earth, along with the human race and the individuals who make it up, are in the cosmic scheme of things, and suggests that we all ought to be kinder to one another. Even if you quote Carl Sagan while delivering them, such comments are pretty vacuous, though at least Thompson’s delivery suggests a bit of a tongue-in-cheek attitude lacking in the rest of the picture.

Among the cast, Elgort (who suffers even more effusively than he did in “The Fault in Our Stars”) and Dever are easily the most affecting, while at the other end of the spectrum Garner overdoes the brutal prissiness of Brandy’s mother. Everyone else falls into the mediocre middle, though it’s at least nice to see that Sandler is still capable of a bit of understatement, and the reliable Greer adds a touch of authenticity to her portrait of a mother who’s entirely too compliant with her child’s wishes. Technically this is a polished product, with a convincingly realistic production design by Bruce Curtis and unfussy but effective cinematography by Eric Steelberg. People who object to subtitles might find the use of graphics of texts, tweets and social-media postings throughout a chore to deal with, but though tiresome they’re germane to the point the picture’s making.

But ultimately “Men, Women & Children” is banality posing as profundity, a sermon so heavy-handedly delivered that it probably won’t even stop bored viewers from checking their cellphones while it’s urging them not to.