It isn’t “obviously true” and you would realise that if you considered the supposition more carefully.

His claims is that every breath you take contains faeces.

Firstly the linked studies show bacteria in the air, bacteria is a component of faeces but do not constitute faeces by themselves.

Secondly every breath? Yes outside of a chip making fab clean room. I see no evidence for faeces in the air in a reasonably clean room. Where’s the source? How are faeces being aerosolised ?

It’s implausible.

But the study outdoors that detected bacteria in American Midwest cities!!! Yea there’s zero chance those cities are near farms where they spray with fertiliser. Zero.