Skeptics (or "sceptics" if you're foreign. Or Canadian.) deal with a lot of things that are more or less entirely untrue. Bigfoot (doesn't exist) and Nessie (doesn't exist, and is probably otters) and other so-called cryptids, ghosts, conspiracy theories, and aliens. That list isn't exhaustive, by the way.
There's a lot of overlap in those areas, and not simply because people who believe in one of those phenomena are likely to believe in others, but because people who espouse them as explanations tend to commit the same logical fallacies, mostly involving the fallacy pictured above.
That picture is a popular internet meme, actually. The man in the picture is Giorgio Tsoukalos, and it's from a History Channel show1, a purported documentary about the mysteries of the past. Tsoukalos typically resorts to another incarnation of the meme.
The only real mystery in the show is why his hair looks like that.
The picture up top refers to the logical fallacy, the Argument from Ignorance, or argumentum ad ignorantium if you're wearing a top hat and monocle.
When there's no evidence, do you know what conclusions you can draw? None. Do you know what you do in response? Investigate with an open mind and see where the evidence takes you. Instead, what UFOlogists and cryptozoologists2 argue is that if you can't prove it wasn't aliens, then it must have been aliens. Or if you can't prove there's no bigfoot, then obviously bigfoot exists. Similarly, creationists tend to feel that if you can't prove their religious proposition false, then it must be true. Even Lisa Simpson was able to point out how spurious that argument is. As the popular saying goes, "You can't prove a negative"3.
When we're dealing with ancient history or obscure phenomena, there usually is a paucity of evidence. What has to happen then is building models based on what little evidence there is. Unfortunately, what happens then is that "[BLANK]-hunters" tend to be anomaly-hunters. Something strange! You can't explain it, therefore I'm right! As you can see, it's the argument from ignorance again, only instead of a lack of evidence, it's the explanation for the evidence. Either way, the supposed inability to disprove a hypothesis is taken as proof of the hypothesis.
In fact, alternative explanations can be provided! Let's look at ghost-hunting; this is a field rife with anomaly-hunting. Ghost-hunters simply aren't investigators. They take all their adorable little equipments and hunt for strange things. EM field! Ghost! ... or wires in the wall. Why not investigate and see if you can't eliminate other possibilities before jumping to "ghost!"? Take photographs and what do you find? Shining dots or lines! Ghost! Except they only show up when you use a flash, and didn't show up before the advent of flash photography. The glowing dots? Dust. The glowing lines? Reflections off straps or bars. Like I said, they've never shown up without a flash, which is why "flash artifact"4 is a better explanation than "ghost".
What about when there's little evidence? Like aliens being the proposed explanation for a lot of phenomena, from crop circles to abductions to cattle mutilations. There are of course explanations for these phenomena. Drunk guys, nightmares, and natural decay respectively. However, alien fanatics love to pull out Occam's Razor; our ONE explanation is better than your three explanations! But that's not how Occam's Razor works. First, it's not actually proof in itself; it's a guide to better logic. Also, Occam's Razor actually supports the skeptics, not the fanboys. The alien hypothesis is singular, but that doesn't make it simple.
Once you open it up and start unpacking it, you find that the alien hypothesis actually contains a lot of assumptions, almost all of which are wildly improbable.
- First, we have only one datum for life. We can make absolutely zero assumptions about the existence of other life. Life could be common, it could be rare, for all we know, we could be unique. We simply know nothing, so the assumption that there's other life out there is unfounded, unwarranted, and decidedly not simple.
- We do know that regardless of how common life is, multicellular life must be far less common. Life on Earth spent billions of years as single-celled organisms. So the assumption of multicellular life elsewhere is another wild leap.
- We also know that intelligent life is even less common, because we have precisely one example on a planet teeming with life, so there's yet another wild leap of assumption.
- Then we start venturing into the ream of fantasy, because the example of intelligent life we have (us) can barely even make it off our planet, and certainly can't colonize, so assuming the extant, multicellular life forms out there are capable of leaving their planet is a fantastic5 assumption.
- And if we were to bankrupt ourselves pouring all our resources into it, we could build an interplanetary spaceship that would take many thousands of years delivering a shipload of corpses to a foreign star, so assuming that that life could travel between the stars is beyond fantastic.
- Then it has to assume that, having made the journey across the unfathomably vast gulf between the stars ... they fuck with farmers by probing them, half-eating their cows, and fiddling with their crops.
Assumption piled on assumption piled on assumption, with an argument from ignorance as the cherry on top. Similarly, which is more likely, that thousands of people hunting the woods have failed to find an elusive species of apeman, or that the apeman doesn't exist?
It's not so much that skeptics want to come along and shit in the apple pie and spoil your fun... it's that you're wrong and you keep saying you're not.
1 - We need to take that name away from them. They suck now. I don't think they deserve "The Mystery Channel" either. Maybe "The Mysteriousnessosity Channel".
2 - Some people think that if you put "-ologist" at the end of something, then that gives you authority and credibility. Unfortunately, when it comes to the general public, they're usually right.
3 - Actually, you can, but its usually a long and exhaustive process. As in you have to exhaust various possibilities until you're left with a single, plausible hypothesis. It's called abductive reasoning. It's what scientists and Sherlock Holmes do. Well, what Sherlock Holmes does when written well.
4 - In science, an artifact is something you avoid if at all possible, and account for and ignore if you can't. If your equipment always records a sudden spike at a certain point in the experiment, it could be something happening to the experiment or it could be something happening to the equipment. The latter always has to be ruled out before the former can be adduced.
5 - As in it's a fantasy.