In the old days, you would check in on an alien-visitation shlock-TV documentary (or an episode of “Unsolved Mysteries”) all to catch those grainy home-movie glimpses of alien spaceships. On that score, “Close Encounters of the Fifth Kind” is nothing less than an all-you-can-eat banquet of UFO porn. There are vintage clips of “sightings” shot in 8 and 16mm, but most of them are from the home-video and cell-phone-camera era, all tagged with important-sounding datelines.

CE5 event, March 16, 2017, Newport Beach, Calif. (five shimmering green lights in the sky!). CE5 Event, Sept. 21, 2019, Vancouver, B.C. (purple lights ringed like an X-ray of bottom teeth!). There are shaky-cam videos of glowing discs that hover and vanish into the ether and what look like a pair of suns that appear on an ocean horizon. There are mysterious lights, sometimes three (in a triangle), sometimes five (in a cluster), or 10 in the shape of a V. As always, these you-are-there images cast a spell, though the most spine-tingling element is often the reactions of the people shooting the video, who always say something like “Ho-lee shit” in a way that makes it sound like they’re witnessing the uncanny.

Of course, after you’ve seen 30 or 40 of these clips, they begin to acquire a certain more-is-less quality. Look, it’s one more set of lights hovering in the sky! One more saucer-shaped thingy! Another blip, another blob, another fuzzy pulsating orb, another streak of light too crooked to be a comet trail. Are these really alien ships? Or are they close encounters of the WTF kind?

“Close Encounters of the Fifth Kind” is the third documentary, following “Sirius” (2013) and “Unacknowledged” (2017), to be centered around Dr. Steven Greer, the apostle of the alien-visitation “disclosure” movement. “Unacknowledged” was a kind of extraterrestrial manifesto, and it’s a movie that can suck you in and give you that down-the-rabbit-hole experience, so that as you watch the footage and scan the hidden government documents and hear the testimonials, you may find yourself on the precipice of feeling that you…believe. In “Close Encounters of the Fifth Kind,” we see Steven Tyler on “The Joe Rogan Experience,” repeating to his host, “You’ve got to see ‘Unacknowledged,'” as if watching that movie would change your life. And that, in a way, is the point of all UFO porn: to provide a conversion experience. (I was blind, and now I believe in ETs!)

But “Close Encounters of the Fifth Kind” treats alien visitations as a given. That is, it totally takes for granted that there’s a technologically advanced, mystically benevolent world of extraterrestrial beings, light-years beyond ours in development and consciousness (though they still walk on two legs and have big bulgy heads like the Martians in ’50s sci-fi movies), who for all their cosmic distance from earth still had enough concern to show up in 1947 to save us from the specter of the nuclear age.

Taking this as undeniable fact, “Close Encounters of the Fifth Kind” is a conspiracy documentary built around the thesis that the “national security state” has concealed it from all of us. It has kept these close encounters hidden in the darkness — and just as deceptively, it has advertised, through the mainstream media and Hollywood movies, the notion that if life beyond earth exists, it must surely be hostile. More “War of the Worlds” than “E.T. the Extra-Terrestrial.” The national security state has done all this for its own world-dominating purposes. “Close Encounters of the Fifth Kind” is two hours of fantasy propaganda attacking reality-based propaganda. It can make your eyes widen and your head hurt at the same time.

With his pockmarked face and broad shoulders, Dr. Steven Greer, who was born in 1955 (and claims to have seen a flying saucer when he was nine), is like a ’70s computer nerd played by John Waters with a touch of Guy Pearce. He’s compellingly articulate, with a thousand points of information and a kind of name-dropping “I was at this meeting at the CIA…” cockiness that lends his statements a patina of authority. With his books, films (this one, like “Unacknowledged,” was directed by Michael Mazzola), and his privately curated group sighting tours, he’s become the science-whiz P.T. Barnum of alien visitation, a role he seems to relish all the way to the bank.

Does he believe everything he says? Part of the strange psychology of our time involves people with vast platforms stating things that aren’t true as if they were true, and doing it often enough that they believe it themselves. When Greer chokes up into an “Oprah” moment and weeps on camera at the thought of all the people on his team who’ve either committed suicide or been assassinated (yes, he says this), you’re seeing a man who will go the extra mile to sell his snake oil. Steven Greer seems sincere and intelligent, but he’s also got a prattling-on-at-the-mouth touch of New Age narcissism, and the narrative he spins is so extreme that you either buy it or you don’t. I’ve always watched those clips of sightings feeling as if alien ships could be real (though what I tend to think is: they’re some form of defense craft), yet Greer, in his way, does a version of what Trump does, taking the fake-news accusations that were once leveled against alien believers and projecting them onto the skeptics. If, like me, you’re not a believer, then you’re perpetuating the lie. You’re part of the conspiracy.

And as “Close Encounters of the Fifth Kind” makes clear, the mythology of alien visitation has become the mother ship of all conspiracy theories, mutating with the times, soaking up other conspiracies like a sponge. The new alien theology is a hydra that keeps sprouting new (paranoid) heads.

There was the original incident, and cover-up, at Roswell. (Several aging military figures who claim to have been there testify, in the movie, that they saw the alien bodies.) There’s the idea — and this goes back to the stories of George Adamski, the founding voice, in the early ’50s, of the alien-contact movement, and also to the classic 1953 movie “The Day the Earth Stood Still” — that aliens have arrived, and they’ve come to be friends, but the government can only see them as a hostile force.

To that idea, Greer now adds a layer of deep-state treachery, claiming that it’s all an underground plot that even the U.S. president has no power over. And this is all linked to the environmental movement — or, in fact, to the systematic squelching of it. One key reason for the cover-up, you see, is that the aliens possess technology that could solve the energy crisis with the snap of an ET finger, nixing the need for oil or even solar panels. (It would all happen with advanced alien tech magic, lending new meaning to the phrase “little green men.”) But naturally, the American fossil-fuel complex will have none of this. Believe it or not, even the death of Marilyn Monroe has been glommed onto the conspiracy. According to Greer, the reason Marilyn was “killed” is that, in the midst of her affairs with JFK and RFK, she was about to say something in public about the government’s alien secrets.

What’s more, remember all those stories in the ’80s about alien abduction — all the folks who looked like future Trump voters who claimed to have been taken aboard alien spaceships and probed while under a state of hypnosis? According to the movie, that’s now part of the conspiracy. The abductions, it turns out, were all staged as an act of counterintelligence. Richard Doty, a sleazy-impish retired agent of the Air Force Office of Special Investigations, claims that it was his job to hoax UFO researchers (there’s a whole documentary about Doty, entitled “Mirage Men”), in part to make them look like wackjobs.

In the ’70s, people got off on the sheer wish-fulfillment awesomeness of close encounters, the whole religious “Whoa!” factor of it. But what the science-fiction-is-real circus of “Close Encounters of the Fifth Kind” is selling is the dream that aliens could save us from the darkness of America. They’ve become sci-fi versions of Jesus crossed with Noam Chomsky. (And does this movie, as it implies, really think that the Russians or the Chinese would be any more humane about it? Vladimir Putin would eat an alien for breakfast.) The movie is predicated on a kind of emotional formula in which deep-state secrecy equals cover-up, and if there’s a cover-up then there must have been something to cover up. The film works like a drug, or maybe the cakes Alice eats in “Alice in Wonderland.” It says to its audience: Experience this movie, and it will clear your mind of the disinformation, laying bear the glowing nugget of revelation under the conspiracy.

But as it goes on, this all becomes a marketing hook for an increasingly flaked-out fantasy. In the midst of his anti-government screed, Steven Greer slips in that there have been many, many extraterrestrials captured and killed, and that in the desert of Arizona “there’s an underground facility where there are nine different ET craft that are there with all the autopsy bodies.” His proof? “There’s a man on my team who used to work in that facility.” He goes on to compare the aliens who’ve visited the earth to Gandhi. And that’s before the movie, in its windy second half (ESP, the physics of teleportation, aliens as mystical avatars of a one-universe consciousness), threatens to become a quantum version of “Koyaanisqatsi.”

The ultimate oddity ­of “Close Encounters of the Fifth Kind” is that it pushes a rabidly pro-environmental, anti-corporate, flower-child agenda, yet it does so with the kind of huckster aggression that has allowed left-wing conspiratorial thinking to mutate into right-wing paranoia. Put another way: The belief in alien visitation, as presented here, is actually congruent with the Trump agenda — the idea that America could be restored in one fell swoop by an acceptance of the otherworldly saviors who are already in our midst. That sounds, in its way, distressingly familiar: a promise to fix the world with fairy tales.