How can you know that hyperdunc is a "pirate"? How can you know that hyperdunc advocates for further "piracy"? His argument is that there is a word for copyright infringement and the word clearly isn't theft or piracy.
A sentinent like "pirates will always find a way to rationalize theft" is unreasonably dismissive and perhaps shaped to protect an ideological position.
This is a question of semantics. You're trying to coopt the gravitas of the word "theft". But theft is the illegal removal of a (physical) item, not copying an item while leaving the original as it is.