Pah. Why are old-people's 'experiences' not also 'plausible-sounding bad ideas' from another time? In fact, that's the only mechanism your pessimism permits.
I'd guess, instead, that these modern bad ideas are possibly good ideas that just don't jibe with your experience.
Currently popular ideas are not the result of a historical meme ratchet, whereby ideas have only been replaced by better ideas. A cursory knowledge of history provides ample evidence that bad ideas have often reemerged and become the orthodoxy of the time, supplanting earlier hard-earned wisdom.
With that history in mind, the common notion that today's popular ideas are all wiser than any of the past can be seen as absurdly unlikely. Does that imply that all old ideas are better than new replacements? Of course not. It implies that some of them are.
It implies that if you are more interested in wisdom than in popularity, you should look beyond what is taken for granted as the orthodoxy of your own generation.
I'd guess, instead, that these modern bad ideas are possibly good ideas that just don't jibe with your experience.