Where I draw the line for whether it is ethical to light things on fire is when they start destroying rare knowledge and books as fast as possible for no other reason than to hoard and obscure knowledge for private benefit.
It is one thing to fund the creation of knowledge and then hoard it, it is entirely another to begin actively attacking and destroying pre-existing publicly shared resources of knowledge in the pursuit of monetizing access to that very knowledge behind a gargantuan profit motivated entity.