[tootie]

I also have yet to see any evidence that hygiene hypothesis is true or leads to better long-term health outcomes.

[Herodotus38]

There's actually pretty good evidence now that childhood sanitation is correlated with the incidence of Acute Lymphoblastic Leukemia (ALL). Edit: accidentally wrote inversely

Here is a pretty good overview:

https://www.medscape.com/viewarticle/897242

Note that this is a little different than the usual interpretation of the hygiene hypothesis.

[kristiandupont]

The book An Epidemic of Absence presents a pretty compelling case, I recommend it.

[gruez]

a 400 page (tl;dr), non-peer reviewed book (no endorsements from the scientific community) is probably not the best evidence to present.