… is from page 194 of Robert Cooter’s 2000 book, The Strategic Constitution :
Legislation often begins with a preamble stating a high purpose and then proceeds with pork-barrel provisions in the main body of the law. Thus the general purposes stated in the preamble have no real connection to the legislation’s substance.
Members of genuinely reality-based communities recognize this reality of legislation and of the politics that produces it. The Fair Labor Standards Act, for example – while sporting a fine-sounding title – is, in substance, shabby interest-group legislation  that has nothing to do with making labor standards “fair.”
(Although it’s behind a paywall, my 2001 review of Cooter’s Strategic Constitution is here.)