> Is there anything else that's covered by copyright that's in a similar sort of situation as software? Where the thing that's covered by copyright _isn't_ really modifiable to begin with?

I don't see how software is unique here. You can modify a compiled executable, just like you can modify a finished graphic, or a produced movie, or a piece of music from an album. It takes additional effort, but so does modifying the graphic without the PSD file, the movie without the editor project files, and the music without the stems.

The original copyright laws date from the 1700s; at the time the only thing being protected was text: stories, essays, reference volumes, etc. Basically, stuff for which there was no "source code" to conceal, the whole thing was right there on the page.

It's only been in the 20th century that we've increasingly seen classes of copyrightable works for which the source code dwarfs the final released product: music, digital visual arts, film, and software

To make matters even worse, the commercial interest in copyright doesn't care about any of this, because pirates only duplicate and distribute the end product anyway. So it's only the creative side wanting to remix and extend that is shut out by all of this.