While I think the hygiene hypothesis makes a lot of sense, we need to be careful about assuming it's correct, because we're working from "this is how it is now,

While I think the hygiene hypothesis makes a lot of sense, we need to be careful about assuming it's correct, because we're working from "this is how it is now, this is how we think it was then, what changed (and can we find examples of it not changing to control with)?" not "this is how it is now, if we do this, what do we think is going to happen?" There's also the next logical followup of "well, if we think/assume/know this is the case, what should we do about it?", and while we're experimenting with a few avenues (deliberate helminth or similar mostly-harmless infection is a surprisingly promising avenue), we're definitely in Early Days of even testing different things, much less suggesting any concrete actions. Growing up, I knew relatively few people with any kind of allergic response at all, minor or major - two of my three younger siblings (the closest 4 years my junior) developed mild (e.g. even if they got scratched they're not gonna need an epipen) cat allergies as they got older, and a couple of their friends have "no really there was a peanut in this room in the last 24 hours probably and That's A Problem" levels of allergic response. That said, it's also a retrospective problem of estimating prevalence of something you didn't really note down the same way at the time as important if it wasn't critical (or if e.g. you didn't have common usage of allergen tests unless someone suspected something - for example, I've not had an observed/suspected allergic response to anything, nor had an allergen panel because it's just...not been an issue).