Anyone who has taken apart both old and modern things has see the design choices the engineers made and they know things have moved from more durable to more inexpensive.
We've witnessed it first hand. It's abundantly clear, and no amount of gaslighting is going to get us to disbelieve what we've personally experienced.
Equally important though is that old things were much more repairable than the things we have now. This does make them **seem** more durable because they stick around for generations until eventually replacement parts are no longer available. But the hilarious thing about it is that they don't frequently **need** repaired. Ironic.
You'd have an easier time arguing that it's good that things are no longer made to last. One could argue that prices are lower, things are more readily available, and that the disposability is good because it creates more jobs (scraping things for metals to recycle, sales people, shipping companies, trash service, etc.). Perhaps the fact that they don't last as long is compensated by being able to buy multiple of them for the same price and the set of them combined might last as long as one of the old stuff.