> So there is at least some merit to the idea that we just can't build as well as we used to.
We could, there is nothing preventing the US or Europe to return to 1970s taxation for companies and the filthy rich. The reason why we can't build like back then is to a very large part the erosion of the tax base to pay for it.
The data does not support your claim. US government expenditure as a fraction of the GDP was lower in the 70s (30-35%) than it is now (35-40%). The government revenue, about the same (around 30%). So the tax base is roughly the same relative to economic output, and spending slightly higher, with the difference made up for by deficits.
The Transcontinental Railroad was built in the 1860s and the Hoover Dam in the 1930s, both when government expenditure as well as taxation at all levels were a single-digit percent of GDP. I suppose by your logic we would be a galaxy-faring species if only we were able to tax the likes of Bezos and Musk?
We could, there is nothing preventing the US or Europe to return to 1970s taxation for companies and the filthy rich. The reason why we can't build like back then is to a very large part the erosion of the tax base to pay for it.