At the start of Alexander Payne’s new film, a scientist-entrepreneur proclaims a vision of saving humanity, and the planet, by shrinking people down to few inches to minimize consumption and environmental degradation. By the end, the emphasis has shifted to the importance of individuals helping individuals: instead of trying to save everybody and everything, why not try to alleviate one person’s misery a bit? The real “Downsizing,” Payne suggests at the close, should be in the form of unrealistic ambitions—don’t try to save the world in the abstract at one fell stroke, but concentrate on helping one actual human being at a time.

Like its protagonist, a good-natured schlub named Paul Safranek (Matt Damon), the film reaches that realization via a circuitous route. Stately and quiet, it begins at a scientific conference on sustainability with Norwegian entrepreneur Dr. Jorgen Asbjornsen (Rolf Lassgard) announcing his firm’s success in achieving its long-sought goal of bodily miniaturization and introducing its first happy results, a small cart of tiny folk, to an astonished world. People will be recruited to undergo the procedure through information about its benefits it holds for the world at large, but also via more practical forms of motivation, since one’s assets at full-size will be hugely magnified by becoming a five-incher. The result is that even a middle-class person can afford a mansion in one of the company’s planned communities, and enjoy amenities he could only dream of before, by choosing to be downsized.

That doesn’t initially attract Paul, who once hoped to become a doctor but wound up as an occupational therapist, or his wife Audrey (Kristen Wiig), but after they encounter a couple of high school pals (Jason Sudeikis and Maribeth Monroe) who have gone small at a class reunion, they begin considering the option. Impressed by a company tour hosted by ebullient spokesman Neil Patrick Harris and his wife (Laura Dern), they decide to take the irreversible leap and prepare for a move into a mansion in upscale Leisureland.

Unfortunately, things do not go as planned. Audrey chickens out at the last minute, leaving Paul on his own in the new, smaller world, and their divorce reduces him to taking an apartment. His search for female companionship leads nowhere, but he does make the acquaintance of his hedonistic upstairs neighbors Dusan Mirkovic (Christoph Waltz) and Konrad Joris (Udo Kier), who introduce him to celebrities and new pleasures. His visit to their apartment also leads him to something else he wasn’t aware of: a dark underside to the entire downsizing program, an off-the-grid ghetto inhabited by folks like Ngoc Lan Tran (Hong Chau), a handicapped Vietnamese dissident who works as part of the cleaning crew serving the well-to-do. It’s his engagement with this plain-spoken, hard-working and extraordinarily compassionate woman that challenges Paul to rethink his beliefs, even after Dusan and Konrad take him on a trip to visit the project’s progenitors, who are about to strike out on a different path.

“Downsizing” will perplex viewers who approach it as though it were something along the lines of “Honey, I Shrunk the Kids” for grown-ups. There are aspects of the film that are quite funny: the Harris-Dern infomercial is a hoot, as is the step-by-step depiction of the miniaturizing process, staged like a crazy form of assembly-line medicine; and you can’t help but smile at Damos’ blasé cynicism (perfectly conveyed by Waltz) and Ngoc Lan’s bluntness (which Chau spits out with nonchalant vehemence).

But Payne and his writing partner Jim Taylor have more on their mind than just amusement. Ultimately their aim is to argue that if the world is to be improved, it will require changes in basic attitudes rather than in contriving new ways of doing the same things we do now. As they depict it, the downsizing program is the equivalent of a pill that allows one to go on living the same unhealthy way one has always done—a simple, undemanding means of avoiding really significant change in ourselves. It permits a person to live in miniaturized form the life he’s always wanted to live—large. That’s its fatal flaw.

There are some problems with the way in which Payne makes his point. One is the leisurely pace of the film (edited by Kevin Tent), which may strike viewers as dilatory. Just as seriously, as played by Damon in ultra-subdued style, Paul comes across as denser than he ought to be; he must be awakened, but perhaps not from so deep an intellectual slumber—though admittedly it’s enjoyable to watch Waltz, Chou and to a lesser extent Kier shake him into confronting his own failings. On the other hand, Wiig is wasted in a thankless part, and the rest of the supporting cast offer only passing moments of pleasure.

It has to be added that technically the film is impeccable, with standout contributions from the effects team supervised by James E. Price as well as production designer Stefania Clark and director of photography Phedon Papamichael. Rold Kent’s score is also unobtrusively effective.

In “Downsizing” Payne is, ironically, working on a larger scale than in the past, but his sharply honed focus on human foibles and failings remains intact. One fears that the coolly detached approach of the film will distance it from the mainstream audience, but that will be their loss; Payne continues to be one of our most incisive, acutely observant filmmakers.