Stoves may be a bad example, but there are plenty of things that they don’t make like they used to. Without even leaving the kitchen, we can give many examples:
Pyrex measuring cups. Formerly made from heat-resistant borosilicate, they are now made of lime glass—and therefore have a far greater chance of explosively shattering (and potentially inflicting serious injury on anyone nearby) when used with very hot liquids (especially ones with a high specific heat, like sugar syrups).
Cast-iron fry pans. Very old (70+ years) cast-iron cookware is prized on the secondary market, because it was sanded smooth (and thus could be more effectively seasoned, for a long-lasting non-stick surface); modern cast-iron cookware manufacturing skips this step, resulting in a (much less effective) pebbly surface. (And no, this is not explained by retail price reductions; the [inflation-adjusted] price of a cast-iron pan has not changed by more than ~2x since at least the 1940s.)
Heavy-duty aluminum cookware. Guardian Service brand cookware is also prized on the secondary market; nothing remotely like it is made anymore (for example, I once looked into purchasing a modern analogue of a ~1.5-qt. G.S. saucepan, to find that the currently available models have walls literally more than an order of magnitude thinner than the G.S. one; this makes them vastly inferior).
Food processors—specifically, the design of food processor feed tubes. Until ~15 years ago, the gold-standard consumer-grade food processor (the Cuisinart) used an extremely simple design of lid / feed tube / pusher assembly, which was very sturdy, very simple to operate, and very easy to clean. Then they (and every other manufacturer along with them) switched (due to, I believe, liability issues for certain quite implausible injury scenarios) to a new design that was dramatically inferior on practical every axis: much flimsier and more prone to breaking, much harder to clean, much more difficult to use.
Springform pans. Calphalon used to make a flawlessly designed, and very well-built, springform pan, which was manifestly superior in design to every other product in this category. Today, they still make that pan—but they have changed their manufacturing / QA process such that their new pans regularly rust and fall apart within months or weeks of use (the old version could easily last for decades). No other manufacturer makes a comparable product.
Potato mashers. Good luck getting a potato masher like this one today. Currently available models use an inferior design that is far less effective at its task.
It is certainly true that “usually, we moved on for a reason.” The problem is that “we” often means “manufacturers of consumer products, whose goal is to maximize their profits, and who serve to fulfill the values of consumers only to the extent that it maximizes their profits”, and the reason often is “because the new, considerably worse, product is cheaper to manufacture and will sell just as well to uninformed (and deliberately misled) consumers, thus increasing profits”.
The ideal is not a static state where everything lasts forever and nothing ever changes. Such a world is impossible and undesirable—even if we could create it, it would be stagnant. The ideal is a dynamic world of progress, of continual upgrading and renewal.
Your ideal is not everyone’s.
Conclusion does not follow from example.
You are making exactly the mistake which I described in detail (and again in the comments to this post). You’re conflating desirability with prudence.
It is desirable to have as much food as possible, as tasty as we can make it. It may, however, not be prudent, because the costs make it a net loss. But if we could solve the problems you list—if we could cure and prevent obesity and addiction, if we could reverse and prevent damage to our gut flora—then of course having lots of tasty food would be great! (Or would it? Would other problems crop up? Perhaps they might! And what we would want to do then, is to solve those problems—because having lots of tasty food is still desirable.)
So, in fact, your example shows nothing like what you say it shows. Your example is precisely a case where more of a good thing is better… though the costs, given current technology and scientific understanding, are too high to make it prudent to have as much of that good thing as we’d like.
Now this does prove too much. Ok, so “common sense” can’t be trusted. Now what? Do we just discard everything it tells us? Reject all our moral intuitions?
Yes, by all means let’s examine our intuitions, let us interrogate the output of our common sense. This is good!
But sometimes, when we examine our intuitions and interrogate our common sense, we come up with the same answer that we got at first. We examine our intuitions, and find that actually, yeah, they’re exactly correct. We interrogate our common sense, and find that it passes muster.
And that’s fine. Answers don’t have to be complex, surprising, or unintuitive. Sometimes, the obvious answer is the right one.
That is Eliezer’s point.