In English, generic reference takes three possible forms:
A. Cats are cute.
B. A cat is cute.
C. The cat is cute.
But the names of nationalities seem to me to make an exception to this rule. As far as I know, when referring to all the members of a nation, you can only use the C version: The Italians are musical, or The French are posh, or The British are cold.
Why is it that in this case only C is considered grammatically correct? If all the Italians, or all the French, or all the British are musical, posh, or cold, why can't we also say:
A. *Italians are... // *French are... // *British are...
B. *An Italian is... // *A French is... // *A British is...