"The main argument for 'piracy is not stealing' is that there is still an original copy."

No, the main argument for 'piracy is not stealing' is that piracy is not stealing. Stealing is the substraction of property, which piracy isn't.

This isn't stealing either, this is plagiarism.

If we don't name things with their correct names, we create false associations, and that makes arguing about those things needlesly complicated. It's hard enough getting a consensus on anything related to IP as it is, so we should avoid ambiguous syntax wherever possible.