Reasoning by Analogy

One of my pet peeves is reasoning by analogy. Don't get me wrong, it's often a useful pedagogical tool and has some place in science and argument. My problem is that people use it too freely and often grossly overextend analogies and come to strange conclusions.

For example, in Reason this week there is an mildly interesting article on creationism:

So what "speculations" do creationists wish to destroy? In his talk, "Fossils, the Flood and the Age of the Earth," Dr. Tas Walker, a former Australian mining engineer, takes a whack at old Earth geology. Walker says that Noah's Flood is needed to produce fossils. Why? The conventional explanation for how fossils form is that, say, a dinosaur dies, falls into a swamp or ocean, and sinks to the bottom; there the bones are covered by layers of silt and eventually turn into stone.

Walker says that this scenario is very unlikely. He illustrates his point with the humble example of what happens to a dead fish in an aquarium. Dead fish don't sink; they are eaten by other aquarium denizens, leaving nothing to fossilize. As further evidence, Walker adds that nature documentaries showing the bottom of the oceans do not find it littered with the bodies of dead fish waiting to be fossilized. The only way to fossilize a dead fish in an aquarium is to dump a bunch of concrete on it before it's eaten. QED, Noah's Flood was the moral equivalent of dumping concrete on all the fossilized animals found in rocks today.

Since it doesn't happen in my fish tank, it must be impossible even if you have trillions of organisms over millions of years...

He should be made to wear an asshat.