Chris Bertram of "Crooked Timber" is "pretty revolted by the suggestion that one day we might synthesize all our food," although he can't exactly say why. After some Orwell-quoting bloviation about humanity's "engagement with the natural world", he writes, "I just wish I could better articulate exactly what it is" that makes him so passionately "want [his] potatoes from the earth and [his] apples from a tree."
Well, I'm always happy to help out. To begin with, the "natural" or "traditional" foods with which we are familiar are typically tastier than their artificial equivalents, because in most cases the only reason for the latter's existence is as an inexpensive ersatz substitute for the former. Unsurprisingly, many people therefore automatically associate "natural" with "high-quality" and "delicious", and "artificial" with "low-quality" and "semi-palatable", ignoring the exceptions. (A good counterexample is ice cream: the best brands may be high in natural ingredients, but there's still nothing the least bit natural about solidifying sweetened milk products in a freezer. Likewise for "old fashioned" seltzer.)
Of course, properties such as "natural", "high-quality" and "delicious" are also associated with "expensive", and we should not discount the social motivations that tempt many people to insist that less-than-authentically-natural foods (or clothes, or furnishings, or anything else) are simply unacceptable. Add to the mix the fact that understanding the distinction between "natural" or "authentic" and "artificial" or "ersatz" can require considerable knowledge (if only of the most current folklore and fashion), and we have an ideal vehicle for snobbery.
Finally, in the modern industrial world, "nature" cannot but retain an element of exotic glamor. The fable of the country mouse and the city mouse nicely illustrates the inevitable allure of unfamiliar environments with obvious temptations and hidden drawbacks. But now that practically everyone's a city mouse, the enormous disadvantages of a "natural" existence--discomfort, isolation, danger, tedium, economic unviability, ceaseless exhausting labor, the ruthlessness of the elements, the perennial toll of sickness, injury and scarcity, and all the rest--are easily forgotten. Likewise, "unprocessed", "unadulterated"--i.e., unpasteurized, uninspected, and unfortified--foods retain something of the the unrealistic appeal of wild, untamed nature.
We live in an era in which the production of our food has been almost completely industrialized, for better or worse. How many modern-day Prousts, for instance, could be moved to recall the evocative taste of a cookie adored in childhood that did not come from the supermarket wrapped in a package? Under these circumstances, then, it's entirely understandable that rarer, more expensive, more exotic "natural" foods would acquire a special cachet not bestowed upon their mass-produced counterparts. On the other hand, it would be foolish to exaggerate either the depth or the significance of this particular sentiment.