"Guilt" should not be a part of this discussion, it you understand how markets work. Sale of expired film is a perfectly normal market adaptation to imbalances between supply and demand in the fresh-film market. Sellers would always rather sell the higher-priced fresh stuff, but production and consumption will never be perfectly calibrated, so surplus production eventually finds its way to the expired market or is destroyed.

Buy what suits your needs and wallet from wherever you can get the best price, and let Kodak / Ilford / Fuji / Adox worry about the rest. This is precisely the beauty of a market economy; individuals make millions of disconnected decisions which, in the aggregate, signal what the manufacturers should supply, and at what price. We users don't have to fret about the Big Picture; supply and demand take care of that. And no, as an individual out of millions, You Are Not That Important. However, side by side with millions of similar individuals making choices, you are the driver of the whole economy. So elegantly simple.

Orders placed filter up the distribution chain to, say, Kodak, signaling how much product it should make. If retailers aren't selling much "fresh" film because the world's momentarily awash in cheap expired film that everyone's buying, that's a signal to Kodak that either their price is too high for the fresh stuff relative to their customers' other choices (expired, or another maker's cheaper product); or their production is too large relative to demand. Kodak'll slow production of their "fresh" films until the market absorbs the surplus, or until the rate of production of "fresh" film mates up with the rate of consumption of fresh and expired film. That's an equilibrium of sorts, and is probably where things are most of the time.

Once expired film stocks get low, their prices would tend to rise and some buyers would return to fresh film as their first choice. The resultant uptick in demand signals Kodak to raise prices and make more fresh stuff at a higher price. Naturally, they want to sell all they can at a higher price. But larger production means more supply; and higher prices would drive more users to Ilford or Adox, meaning more of this production spurt ends up in the expired-film pool, and demand for fresh stuff falls once again. Because a perfect coupling of supply and demand, signalled by price, is impossible, these market oscillations are continuous, with greater or lesser amplitude, at all times.

Cool, isn't it? A self-regulating decentralized system, when left alone to work.