Ten Issues for Hard Science Fiction" as seen from the perspective of someone living in the year 1800, but then I followed the link to "Where Is Everybody?", Stephen Webb's book about the Fermi Paradox.
I like to write science fiction stories that are set in what I call the Exodemic Fictional Universe. The basic assumption for such stories is that extraterrestrial visitors from other worlds have been visiting Earth for a long time. However, as Man Bin warns, that does not mean that "UFO sightings" are evidence of those visitors.
In my fiction, I like to imagine that Earth has been visited by extraterrestrials who find it trivial to hide from us. Even if an accident happens and someone on Earth notices the visiting extraterrestrials then it is a simple matter to erase memories of the Earthlings who saw something that they should not have seen.
However, in my stories Earth is not crawling with herds of extraterrestrials. I like to imagine that the visiting extraterrestrials are content to mostly watch the course of events on Earth. The opportunities for us to notice their presence are few and far between. Does that mean that the visitors are irrelevant to human affairs? No. For example, in The Start of Eternity the human species was created by the artificial design of space aliens who wanted to make an ape that was similar to themselves.
If aliens with god-like powers have created us and are watching over us, then why do we have so many problems here on Earth? One fun possibility that is explored in The Start of Eternity is that the aliens were doing just fine, but then something went wrong and their "little science project" on Earth went out of control. If you want to know what could "go wrong" for god-like extraterrestrials, read the story...or better yet, help write it!