Were the sea pirates of the 17th century infringing on copyright? No they weren’t. Weren’t they pirates then? Yes they were.
The high seas were uncharted territory in the 17th century, and sea pirates of the time were contesting the rules that sovereign European states were attempting to impose on water, via the use of the monopolistic East and West India companies. Similarly, if you conceive of the airwaves in the first half of the 20th century as uncharted territory, you will observe the same pattern: sovereign states attempting to impose their own (broadcasting) rules using monopolies (such as the BBC), while pirate organizations (pirate radio stations) opposed them and proposed alternative norms of exchange.