This article makes it seem like he personally investigated the cases, he didn’t. What he did was help publicize them and write long book length summaries of the evidence to convince people. He also published a “pamphlet” on Belgian colonial exploitation of the Congo. He worked directly with the lawyers / investigators to get the facts and used his fame and writing ability to get public attention.
I remember reading this in the 90s in SciAm which was supposedly linked to his deep resentment of scientific community in general.
Imagine what you believe in now that will seem fanciful in a century.
"The second paleo era"
The corollary is that when you believe something people think is silly, like that faeries exist, they may be wrong. This is particularly tricky with beliefs like this one which are technically impossible to empirically disprove.
Being able to trust others in their understanding is helpful but it's probably not going to help you sleep at night trying to figure out what you know and what you don't.
And I believe that from a bio-mechanical (muscular, skeletal) point of view, insect-like wings capable on sustaining flight are not possible on a human back.
For an interesting take on this, see the Artemis Fowl series of books where fairies don't have actual wings but are much more advanced that us regular humans, and fly thanks to technological winged backpacks, and this is the origin of the human myth of fairies (they started hiding after middle age, thus why the myth stayed intact).
I guess I'm using a definition of "supernatural" like Richard Carrier's: "mental things [that] cannot be reduced to nonmental things" (http://richardcarrier.blogspot.com/2007/01/defining-supernat...).
So under this definition wizards, psychics, ghosts and gods are all supernatural; but Bigfoot, UFO abductions and fairies aren't.
The Artemis Fowl series is great. Although in the context of this discussion I find it funny that the fairies do have magical powers, it's just that flying isn't one of them.