Extended analogies are like extended sinning, which is itself an analogy of sorts. [LINK]
At any rate, here's my latest letter to the Globe:
Agreeing with a previous letter that it was inappropriate for Ellen Goodman to compare skepticism over global warming with Holocaust denial, Mark MacMillan substitutes another analogy: that of a patient unwilling to believe a doctor's diagnosis of a life-threatening disease because the symptoms haven't yet become obvious. I found this medical analogy far more compelling, but perhaps not for the intended reason.
Imagine learning that you have a slightly elevated level of something that at much higher levels might be fatal. You consult a doctor, who says it's a clear sign of dreaded Malady X, that there's no reasonable chance it could be anything else, and that one of your organs must be removed at once. You'd still be able to survive without the organ, but only with considerably depleted energy. Imagine furthermore that Malady X has never been directly observed, so instead of relying on narrow tests like biopsies and angiograms, conjectures must be based on computer models of the latest understanding of how all bodily processes work together. The doctor further offers no good reason to think that you might actually suffer from the malady anytime soon, or even that removing the organ would prevent its onset.
Now imagine getting a second opinion from another doctor who says that the instruments used to measure the substance are often inaccurate, that levels vary naturally from one person to the next, and that at any rate they are within normal range. She says that even if it were a problem, it could be due to any number of factors. Even so, the symptoms of Malady X are not as bad as once thought. Since it's a definite concern, though, she recommends a period of close observation and further tests.
While such analogies are always clumsy, I hope this helps explain how a reasonable person might be skeptical over various claims of impending catastrophe without being in thrall to quacks and shills. I'm truly sorry to learn that people close to Mr. MacMillan died because they didn't aggressively act upon their diagnoses. But then again, not every bout of heartburn is a heart attack.