Heirloom seeds, by some definitions, are seeds developed at least 50 years ago, making them well-adapted to organic growing conditions since all farmers and gardeners used organic methods then. Makes sense, but I hadn't put that part of the equation together.
I then went on to wonder whether we shouldn't redefine heirloom seeds as seeds developed prior to World War II. For it was during the post-war retooling of the chemical factories that agri-chem warfare was launched, radically transforming our relationship to plant pests and diseases.
Fifty years ago places us in the heart of the post-WWII "better living through chemistry" era. Like so many other falsehoods sold to us in those days, we've had to learn the hard way that heirloom seeds can't be replaced by laboratory creations without serious long-term consequences. And, the "old ways" of doing things -- saving seeds from year to year -- weren't necessarily worth jettisoning.
It's wise to evaluate what's best -- for today and tomorrow -- before committing to a course of action. That used to be obvious.