I have Celiac, so I particularly hate gluten. But I recognize that for most people, it’s innocuous - it’s just a grain protein that I and some other people have a particular problem with, for no real reason. I’d love if American society (and plenty around the world) would de-emphasize wheat and barley vs. other grains, as often wheat flour is used in dishes simply out of habit or convenience. It’s also particularly bad the way the US does the glyphosate ‘dessication’ bullshit, but that’s not about gluten itself.

Anyway, ‘why do people like drugs’ is a very different question. Your premise that people get no benefits from them is technically correct in a long-term view, I guess… but most people aren’t looking at “will I be glad I drank beer 50 years from now?”. Sometimes people manage to consider that their lives would be better without a certain substance, and can see harm in the present - other people actually don’t ever have any issues with a substance and it’s a net positive, for them.