Statistician Andrew Gelman makes an insightful remark, one to keep in mind not just when reading published scientific papers:
Levitt buttresses his argument with the statement, “Chris Goodall [the person who made the walking/driving comparison] is no right-wing nut; he is an environmentalist and author of the book How to Live a Low-Carbon Life.” How relevant is this? Even a “right-wing nut” could make a good point, right?
More to the point, I think we have to be careful about automatically trusting “crossover” arguments. Do we have to believe something, just because it comes from somebody who we wouldn’t expect to say it? I worry that this sort of crossover appeal is so appealing that otherwise-skeptical commentators (such as Levitt) forget their usual skepticism.