Such disparities are a consequence of the fact that, with the exception of infant formula and some baby foods, package dates are unregulated by the federal government. And while some states do exercise oversight, there's no standardization. A handful of states, including Massachusetts and West Virginia, and Washington, D.C., require dating of some form for perishable foods. Twenty states insist on dating for milk products, but each has distinct regulations. Milk heading for consumers in Connecticut must bear a "Sell by" date not more than 12 days from the day of pasteurization. Dairies serving Pennsylvania must conform to 14 days.So in actuality, the meaning of the date is a very complex phenomenon that is specific to the individual traits of the food and the intended quality level, and yet it is one that we seem to work with very well.
That dates feature so prolifically is almost entirely due to industry practices voluntarily adopted by manufacturers and grocery stores. As America urbanized in the early 20th century, town and city dwellers resorted more and more to processed food. In the 1930s, the magazine Consumer Reports argued that Americans increasingly looked to expiration dates as an indication of freshness and quality. Supermarkets responded and in the 1970s some chains implemented their own dating systems.
The Slate writer sees this all as a problem that needs to be fixed, while acknowledging that people seem pretty good at deciding when their food is good to eat. She also raises concerns about the next E. coli outbreak, but last I checked those (as seldom as they are) are probably even less likely to originate from you not throwing your milk away sooner.