What they’re going on and on about is certain varieties and classics of plants/vegetables/fruits/grains essentially going extinct because the seed production world is always on the treadmill to produce the ‘latest and greatest’ varieties.
Some people with organic fixations go overboard, but it is a valid issue. There’s no reason to give up the varieties and selective breedings that have worked well in the past simply because no one took the time to produce them. A great example from the hay industry: oat hay is pretty good stuff for horses. Years ago, there used to be a variety of hay oat called “Swedish Select” — big, fat beautiful leaves, soft stems, which made for great hay. But the grain production on SS was poor - about 40% of what a common dual-purpose Cayuse oat variety is.
Nowadays, you can’t find Swedish Select oat seed - no matter what you’re willing to pay. Because the grain production was low, the seed production potential was low, so growers quit growing it. I know plenty of hay producers who are wishing that they’d kept back some of the crop to combine off the grain for seed for successive years - they assumed that they’d simply be able to keep getting the seed. Their assumptions turned out to be wrong, and now the variety might well be gone...
Many, if not most, of the modern seed stock is hybrids.
They are either infertile or have very poorly reduced fertility and viability.
I try to save seed from my garden, and usually get the best ones from the plants that I grow from the seeds I got last year... what grows the best year over year.
So in a sense heirloom seeds are the Mutts of the seed world!