It's Copyright Week, and I've kicked it off with a post at the Electronic Frontier Foundation's Deep Links explaining why, regardless of copyright term extension, Mickey Mouse will probably never be "free" -- but that doesn't mean that Disney is acting irrationally in its fight as hard as they are for eternal copyrights.
Rather, they're acting in their cold-blooded self-interest, playing a very long game indeed.
But at that point, we expect that Disney will try to use another body of law to suppress creativity and commerce involving Mickey Mouse, whether or not "Steamboat Willie" and "Plane Crazy" are in the public domain: trademark law. If you sell something Mickeyish—including its public domain cartoons—Disney might ask a court to stop you because people who buy the
cartoons from you may think they're buying from Disney. Back to court with you!
Disney would be wrong, according to current law. The Supreme Court ruled in 2003’s Dastar v. Twentieth Century Fox Film Corp. that you can’t use trademark law to extend an expired copyright. But we suspect that with the copyrights on many iconic films and characters poised to expire, Disney and friends will try to get Dastar overruled or at least undermined.
If you want to make a new Mickey Mouse thing, you might be better off arguing fair use than public domain, anyway. Fair use covers transformational use for commentary, parody, education and many other uses. If you're trying to make new Mickey stuff with the "public domain" Mickey from the 1928 cartoons, you'll have to be careful not to encroach upon the visual elements of Mickey that Walt Disney, Ub Iwerks and the other artists who worked on the shorts developed over time in other cartoons that are still under copyright. Fair use has no such constraint.
We'll Probably Never Free Mickey, But That's Beside the Point