There is a very large organization out there who pays in those dollars and demands taxes in those dollars. If you want to live in a certain piece of dirt, you will deal with that organization.
That dirt is very tangible. So is the vast organization running that dirt: it builds roads, runs a military, and (in extreme cases) sends out people with guns if you don't pay those taxes.
I think the point being made is that we assign a value to arbitrary things. People often cite cryptocurrency as not having real tangible value but the same could be said about anything we collectively assign some value to it.
I'd further argue that nothing truly has tangible value because by definition, value is an intangible concept. The question isn't whether it's tangible, but whether its value to risk ratio is good enough for you.
