I really, really hate to play Devil's Advocate, but certain hardcore WP'ers actually do have a point about the worldwide overextension of copyrights. Their solution, which is to grow a collection of low-quality public-domain content from the ground up, isn't the optimal one or even a good one, but in the face of corporate near-control of the political process required to "liberate" older works from the copyright system, it's something publishers should have predicted before they started demanding the extensions. (Of course, that would have required long-term thinking.)

In reality, it seems to be a case of a few large 'n' greedy megacorps (Disney and Time-Warner, for example) holding everything else hostage because of their demands to control everything they currently hold in near-perpetuity, and publishers like the Encyclopedia Britannica just coming along for the ride.

I doubt it's as significant an effect on the intelligence of the general public as, say, the anesthetization of people by a constant barrage of trivialized and sensationalized TV and other mass-media... But if we grant the possibility that much of the user-generated content we're concerned with here (not just Wikipedia) wouldn't have been necessary to set up in the first place if copyrights weren't being blanket-extended to ridiculous lengths, then it's probably worth mentioning, IMO.