Preaching to the choir rarely makes for good theater, but having one’s beliefs reaffirmed can at least carry a cheap buzz if the sermon is compelling enough. Sadly, though, “Walmartopia” hammers away at the safest of topics with a dismaying lack of finesse, determined to convince audiences that underpaying employees and squashing free thought are, in fact, bad. Originally a 40-minute mini-musical before its successful run at last year’s New York Fringe Festival, this plodding tirade at the big-box behemoth strives for little beyond inoffensively wacky populism — and falls short even by those terms.

The Fringe Festival alumnus “Urinetown,” with its cheeky blend of toe-tapping agitprop, is the clear template for co-writers Catherine Capellaro and Andrew Rohn. But while that show acknowledged the ridiculousness of its protagonists, Ms. Capellaro and Mr. Rohn offer up Vicki Latrell (Cheryl Freeman), a saintly African-American single mom, without even a jot of irony. Vicki and her headstrong daughter, Maia (Nikki M. James), live in a fleabag hotel in Madison, Wis., barely able to survive off their combined Wal-Mart earnings. A botched attempt at turning the two into company spokeswomen results in a confrontation between Vicki and the board of directors, with atypical results: A mad scientist (Stephen DeRosa) tosses her and Maia into a time machine fueled by the disembodied head of Sam Walton himself.

While this oddball notion has some promise, the resulting conceit couldn’t be more predictable: the two women find themselves zapped into an Orwellian police state circa 2037 that includes among its subsidiaries School-Mart, Med-Mart, and News-Mart. The lone holdout from the store’s global spread is Vermont, which seceded from America in 2009.

Vicki and Maia, previously cast as adoring Wal-Mart employees, now find themselves playing “two-bit syrup tapper” terrorists in a jingoistic broadcast designed to rally support for a company-led invasion of the Green Mountain State.

Notwithstanding that disembodied head, the presence of the company’s ubiquitous smiley-face logo all over David Korins’s set, and Miranda Hoffman’s costumes, very little in “Walmartopia” feels specific to the business practices of Wal-Mart as opposed to those of any other labor-unfriendly corporation. The real villain here is bottom-line-crazed Big Business, and only a few tweaks here and there differentiate “Walmartopia” from, say, “Costcopia” or “Targetopia.”

Ms. Capellaro and Mr. Rohn’s score is similarly generic, sticking within the realm of pastiche — tepid R&B for the two African-American characters, country for the Arkansas-based board of directors. (The lyrics are a bit sharper, at least when Vicki and Maia aren’t singing about their “crazy, crazy dreams.” The villainous executives get some of the sharpest material: “Someday the meek will inherit / Till then I don’t have to share it.”)

That any of this material makes an impact has less to do with Daniel Goldstein’s slack direction and more to do with his uniformly strong cast. Ms. Freeman and Ms. James have a natural mother-daughter chemistry, and Bradley Dean fares well as a pair of confederates. Mr. DeRosa channels Martin Short’s water-limbed antics capably and finds additional laughs as a near-catatonic extra in the anti-Vermont production, and John Jellison is a deadpan treat as the head of what Maia calls the “creepy Christian crypto-fascists” at the head of the world’s largest private employer. If that line is sufficient to get your blood boiling, “Walmartopia” is for you. More discerning customers are encouraged to do their shopping elsewhere.

Open run (18 Minetta Lane, between Sixth Avenue and MacDougal Street, 212-307-4100).