Were American science-fiction movies ever as fertile and frantic as they were in the 1970s? The one-two punch of Stanley Kubrick’s “2001: A Space Odyssey” and Franklin J. Schaffner’s “Planet of the Apes” in 1968 kicked off more than a decade’s worth of sci-fi flicks that were tough, smart, and full of ferocious social commentary. Goodbye to ’60s trash such as “Robinson Crusoe on Mars” and hello to ’70s social satire such as “A Clockwork Orange,” “The Stepford Wives,” and Woody Allen’s “Sleeper.” It was an era when producing a big-budget version of Kurt Vonnegut’s “Slaughterhouse-Five” seemed like a good idea, but it also sowed the seeds of its own destruction, birthing four film franchises — “Star Wars,” “Star Trek,” “Mad Max,” and “Alien” — that would deliver diminishing returns throughout the ’80s and usher in the era of immense merchandising that saw smart sci-fi movies mutate into idea-deficient blockbusters.

The turning point came in 1982, when “Blade Runner” went toe-to-toe with “E.T.: The Extra-Terrestrial,” and Ridley Scott’s dark, dystopian vision of the future was pounded into pulp by Steven Spielberg’s cute, candy-munching puppet. It’s a bitter irony that “E.T.” sported some of the most successful product placement ever seen, whereas almost every single company featured in “Blade Runner,” from Atari to Pan Am, soon went out of business.

In the 1970s, science fiction was crafted from the raw fumes of decaying 1950s pulp novels, filtered through Rod Serling’s moralistic “Twilight Zone” television series. The results were socially aware movies such as “Soylent Green,” which is being reissued on DVD today by Warner Home Video along with two other ’70s sci-fi classics, “Logan’s Run” and “Outland.” Made in 1973, Richard Fleischer’s “Soylent Green” is set in an overpopulated New York City caught in an endless heat wave caused by the greenhouse effect, and the only foods available are sold by the Soylent Corporation: Soylent Red, Soylent Yellow, and the new flavor, Soylent Green. Charlton Heston, back when he was an anti-war, pro-gun-control, Kennedy liberal, plays Detective Robert Thorn, a corrupt cop investigating the murder of a Soylent board member. But Thorn is mostly interested in looting the dead man’s apartment and having fun with the guy’s nubile “furniture”: a concubine who comes with the lease.

Sexually frank and shockingly brutal, “Soylent Green” may creak in a few places, but it’s more than redeemed by its bleeding heart, which arrives in the form of golden-age Hollywood character-actor Edward G. Robinson. In his 101st and final performance, Robinson plays a “police book,” an intellectual assigned to do research for the illiterate Thorn. Robinson would die of cancer nine days after “Soylent Green” wrapped, but the 80-year-old actor had lost none of his chops in the months before his passing, and you’d be hard-pressed to find a lump-in-the-throat moment to rival his character’s reaction when he realizes that a pilfered stalk of withered celery is the first real vegetable Thorn has ever seen. “How did we come to this?” he weeps in a sentiment that echoes throughout ’70s science fiction.

Also reissued on DVD today is Michael Anderson’s 1976 film “Logan’s Run.” In a tightly regulated future, citizens are exterminated when they turn 31 in a bid to control overpopulation, and are kept ignorant of their fate by a constant diet of sex, drugs, and video games. Michael York plays Logan, a police assassin (called a “Sandman”) tasked with exterminating people who try to escape before their expiration date. But when he goes on the lam himself, the audience embarks on a fabulous ’70s quest through a delirious world of jumpsuits, psychedelic special effects, and enormous sets that look like Disney’s Epcot Center. Sadly, the film is too bloated to deliver any thrills beyond its future-schlock art design, and it is damning evidence of the movie’s shoddiness that Michael Bay would subsequently use it as a blueprint for his 2005 snoozer, “The Island.”

But everything old is new again. These days, “Blade Runner” is hailed as a masterpiece, and while the furniture in “Logan’s Run” may have looked dated in 1985, today you’d pay through the nose for it at a SoHo boutique. Now that the environment has been thoroughly degraded by corporate greed, a movie such as “Soylent Green” looks more socially aware than shrilly alarmist, and even a solid B-picture like 1981’s “Outland,” one of the earliest DVDs ever released and now reissued in a better-looking disc today, manages to achieve more depth with less effort than today’s big-budget flash like “Transformers.”

A weary scrap of anti-establishment grunge, “Outland” is anchored by Sean Connery as a middle-aged federal marshal on an off-world mining colony, abandoned by his family. “Transformers,” on the other hand, is anchored by a digitally generated robot that can turn into a truck. Both films are mass-market movies with no delusions of grandeur, but “Outland” still feels fresh almost 25 years later because it’s about a man and his shotgun taking a stand against evil middle managers. “Transformers” is about selling toys.

One can determine the value of a movie by how it’s remembered, and even today everyone remembers that, as Thorn screams in the iconic final line of the film, “Soylent Green is made out of people!” Meanwhile, less than three months after its release, I can’t find anyone who can coherently describe to me the plot of “Transformers.” The 1970s may have been hell on hairstyles, but they were a high-water mark for socially conscious science fiction. Back then, space was the place where you took on the Man. Today’s carefully engineered, corporate sci-fi flicks are the Man.