Henry quoted The Demon-Haunted World by Carl Sagan
How can we make intelligent decisions about our increasingly technology-driven lives if we don’t understand …
Perhaps when everyone knows that gods come down to Earth, we hallucinate gods; when all of us are familiar with demons, it's incubi and succubi; when fairies are widely accepted, we see fairies; in an age of spiritualism, we encounter spirits; and when the old myths fade and we begin thinking that extraterrestrial beings are plausible, then that's where our hypnogogic imagery tends.
— The Demon-Haunted World by Carl Sagan, Ann Druyan (Page 130)
What he’s alluding to is what humans hallucinate/envision/etc. seems closely connected with what’s “in” culturally. If someone today says they saw a fairy, people would think they’re mentally unwell. But that wasn’t the case in all historical periods, and if people today say they saw an alien - it’s treated seriously.
Most likely, aliens will be replaced by something else in the future when the next thing is “in”