The late, great Bill Hicks had a fabulous anecdote that rather sums up the death of Apollo-era optimism. In 1989, in Fyffe, Alabama, thousands of townspeople and visitors from the surrounding area were reported to have headed out into the night to witness a strange, metallic, triangular-shaped object in the sky. Rather than greeting the first conclusive proof that we are not alone in the universe with wide-eyed awe, Hicks reports with barely concealed disbelief that a number of the townspeople brought guns to defend themselves.

Were attitudes so very different 40 years ago, when Steven Spielberg’s Close Encounters of the Third Kind first touched down in cinemas? Watching the film in today’s political climate of fear and distrust in one’s fellow man – let alone technologically superior beings from the cosmos – it is impossible not to note the glorious naivety of the picture. In Close Encounters, the US army’s reaction to the threat of alien invasion is limited to marking out a site where it is believed the extra-terrestrial mothership might choose to make first contact. The aliens themselves are benevolent, celestial beings who only want to learn more about us, test out our ability to understand basic chord progressions, and so forth. The movie’s early scenes may establish that our visitors’ arrival has the power to terrify those who are not tuned in to their wavelength, but by the time we get to meet them, there is little sense of threat. Ultimately, nobody brings any guns to the ray-gun party.

It is not hard to imagine the outcome if a real mothership landed on US soil today: Trump might well be on Twitter, threatening to nuke it to kingdom come, before our enlightened new friends got to the second part of John Williams’ famous five-note refrain. The pervading, populist cloak of suspicion that envelops the world has fed into our science fiction cinema, too. It is no shock that the most enduring “serious” space saga is Alien, with its terrifying multi-jawed, acid-blooded monstrosities. The slasher-in-space sub-genre is now so much a part of the mainstream that we are subjected to copycat ventures such as March’s Jake Gyllenhaal flop Life.

It seems we are teaching ourselves to be terrified of incursions from another world. A year after the release of Close Encounters, the big superhero movie of 1978 was Superman, the story of a Jesus-like alien who arrives on Earth with the sole aim of stopping really bad stuff happening. Everybody loves him. And why wouldn’t they, when our pant-wearing messiah even has time to rescue cats from trees while repairing fault lines and saving the USA from nuclear apocalypse?

Warner Bros’ recent films about the superhero, 2013’s Man of Steel and last year’s Batman v Superman: Dawn of Justice, essentially feature exactly the same character, bar a little dulling down of the costumed titan’s famous outfit. Yet this time Earth’s citizens are at best utterly terrified of Superman, and at worst would quite like to kill him - immediately - with the help of the nearest batch of kryptonite.

Even last year’s Arrival, on the face of it a pretty optimistic science fiction picture, features a scene in which the local military grunts try to murder the lovely heptapod creatures who are gently trying to teach us useful stuff like psychic time travel. This is the epoch we live in.

The big-hearted Spielbergian sci-fi of the 1970s and 80s is largely dead, despite the best efforts of Christopher Nolan via the ambitious but tonally muddled Interstellar in 2014. We may be another quarter-century on, but Hicks’ description of that UFO “sighting” in Fyffe seems to tally far better with the modern outlook on life, the universe and everything than the wide-eyed sense of wonder exhibited by Close Encounters’ Roy Neary (Richard Dreyfuss).

For Spielberg, the experience of interaction with extra-terrestrials is one of gods, not guns. Neary has repeated, Moses-like visions of a mountain that turns out to be the landing site of the mothership, his sudden, overwhelming sense of purpose likened to a religious experience. The aliens themselves are untouchable, godlike beings, whose presence seems to project a sense of peacefulness and awe – of amazing grace – to all who enter into it. There is never any sense that we should fear them, that those cute countenances might suddenly dissolve into features of warlike menace, the quintet of notes joined by a dissonant, off-key sixth that signals our species’ imminent doom.

Will we ever see the like of Close Encounters again? Fresh off the huge blockbuster success of Jaws two years previously – a paradigm-shifting moment in Hollywood history – Spielberg was in effect given carte blanche with his next project. He could probably have got away with making a six-hour epic about the mating habits of the giant sloth, so high was his standing in Tinseltown. The result is perhaps early-era Spielberg’s most personal picture, one that is even more optimistic in tone than its later companion piece, ET.

The latter film contrasts Elliott’s childlike innocence towards his alien friend with the desire of cynical, coldly painted adults to capture the extra-terrestrial and study him. But in Close Encounters, there are few real grown-ups to be found – just a cavalcade of awestruck Elliotts waiting to meet their best friends from the stars.

• Close Encounters of the Third Kind is re-released in US cinemas on 1 September and in UK cinemas on 15 September