Scientists may not be on board, but 20th century pop culture has never had any problems presenting the ETH as valid. Orson Welles' classic radio play, War of the Worlds, predates the Kenneth Arnold sighting by many years, as does the greatest of all comic book superheroes, Superman, a 20th century icon that also happened to be the Last Son of Krypton (the planet, not the element).
But it was in the 1950s and 1960s that pop culture really began to take the ETH and run with it. Golden Age comics characters such as Green Lantern, who had powers originally based on magic, were re-imagined within an ET paradigm.
Thus, the magical GL Alan Scott of the Golden Age of comics became GL Hal Jordan (above), an Earthman who was recruited into the intergalactic Green Lantern corps, sort of a cosmic Royal Canadian Mounted Police force, run by aliens - the Guardians of the Galaxy.
Batman, perhaps the most terrestrial of all 20th century pop culture heroes, began to have adventures in space, and against villains not of this earth (often working with Superman). The Justice Society of America, with its HQ located firmly on Terra Firma, became the Justice League of America, with an orbiting satellite as HQ (they're now firmly ensconsed on the Moon).
Even Robin Hood, that legendary hero of the Middle Ages, was re-imagined as Rocket Robin Hood, and sent into space, in a groundbreaking cartoon series from the 1960s.
And then came Stan Lee and his pals at Marvel Comics, and we had the Silver Surfer, Galactus, the Fantastic Four, the Kree and the Skrull, and... well, the list goes on and on.
And I haven't even touched on feature films and television (I'm eagerly counting down the days to Star Wars: Revenge of the Sith).
All of this, I would suggest, has paved the way for the general public to accept the ETH as not only possible, but plausible.
This acceptance has had an influence on ufology, and not necessarily a positive one. You'll often hear ufologists quoting opinion polls that show that people are more and more likely to believe that aliens exist, and that they are coming / have come here.
But is this based on informed opinion, with the respondents actually looking at the evidence, or is it based on what they have been reading and watching for the past seventy years?
If the former, why hasn't science hopped on the ETH bandwagon?
Could it because the real evidence is still far from conclusive with respect to the ETH?
Perhaps scientists just don't read enough comic books.
On the other hand, perhaps ufology has become a bit lazy, relying on pop culture and, worse, popular opinion, to make their case for them.