I'd take the pragmatic justification for being copyright-sticklers on
Commons to be: so we can provide a free-media repository that our reusers can use, even commercially and world-wide, in the reasonably secure belief that their reuse is legal, because this is truly freely licensed media.
Compare and contrast to the goal of illustrating an encyclopedia with the best images available, making use of American fair use law to which such illustrations are legally entitled.
Tim Davenport "Carrite" on WP Corvallis, OR