Today James McCormick was found guilty of massive fraud, after pocketing £50m profit from selling dowsing sticks. The "harmless" activity of dowsing is not just carrying around a Y-shaped stick looking for water; like many other ancient superstitions it has been incorporated into New Age nonsense and is used to look for everything from untapped oil reserves to lost golf-balls.
I hope you are thinking "what nonsense"; I expect you followed it up with "but who does it hurt?". The problem is that believing in any pseudoscientific nonsense is a faith-based enterprise, removing evidence and reason from the decision-making process. If someone sells "lost golf ball dowsers" and sells them to the gullible at $20 each, it doesn't do much direct harm. But when society embraces this garbage it can do a lot of harm indeed.
Moving on to James McCormick, he bought up large shipments of the $20 "lost golf ball dowsers", replaced the stickers and then sold them to the Iraqi government at $40,000 each as explosive detectors. The claims were so over the top (it is powered by the user's static electricity, it can detect explosives from the air or even 1km underground, you can reprogram it by putting it in a jar with any other substance to absorb the vapours), that it is obvious to any rational person that the thing was a shame. McCormick even said in an interview that "the theory behind dowsing and the theory behind how we actually detect explosives is very similar".
Unfortunately, we aren't all rational people, and anyone who believes in dowsing for water is hardly in a position to rationally reject the concept of dowsing for explosives. The Iraqi government was so taken with these devices that they replaced physical inspections with dowsing - and people died as a consequence. When confronted with the scam the Iraqi General Directorate for Combating Explosives replied: "Whether it's magic or scientific, what I care about is detecting bombs". And that is exactly the problem. It does matter whether it is magic or science, because science works but magic/dowsing/crystals/prayer/etc do not. Before you laugh too hard at Iraq, more than 20 different countries have bought into this scam, including Belgian police using them for detecting drugs.
James McCormick deserves jail. The greater point, however, is that a society which embraces "harmless" faith-based rubbish is more susceptible to harmful faith-based rubbish. Belief in crystal healing doesn't hurt directly, but it can lead to use of alternative medicines that can kill. Praying to get better from a cold leads to praying to get better from HIV - and hence less diligent use of actual HIV meds. Believing in a God looking out for you makes you more susceptible to lottery scams and the like. And the worst, of course, is when the gullible fools taken in are in positions of power, so we all feel the consequences of their faith-based decision making.