Final answer:
The detail that demonstrates President Roosevelt's faulty reasoning is his assumption that regulated and inspected alcohol would eliminate illicit liquor traffic and generate reasonable taxes.
Step-by-step explanation:
The detail that demonstrates President Roosevelt's faulty reasoning in favor of the appeal of the Eighteenth Amendment can be found in the passage where he states, 'Observance of this request, which I make personally to every individual and every family in our Nation, will result in the consumption of alcoholic beverages which have passed Federal inspection...'.
This demonstrates faulty reasoning because it assumes that if alcohol is regulated and inspected by the government, it will automatically lead to the elimination of the illicit liquor traffic and the payment of reasonable taxes.
However, this reasoning overlooks the fact that during Prohibition, the illegal market for alcohol thrived and organized crime became increasingly involved in the production and distribution of alcohol.'