Why should I care about the public domain?
The short answer is: because you've been cheated. The long answer? Because the movie industry wants you to honor your part of a deal, even though they no longer honor their part of the same deal. You see, the public is being admonished to respect copyrights, but the copyright holders have not respected the public domain. Instead, they have lobbied for extension after extension, indefinitely delaying their obligation to release works into the public domain. This runs contrary to the "limited time" restriction in the U.S. Constitution, and has effectively killed off the public domain.
What is the problem?
The problem isn't copyright itself. The founders of the United States had it right, and struck a fine balance. Copyright originally lasted 14 years with 1 option to renew for an extra 14 years. That is long enough for the owner of a copyright to profit from it, but short enough that the public could reclaim their culture while they were still alive to appreciate it. But now, copyrights can last the lifetime of an author plus 70 years. And that's a problem! The end result is that nothing created since 1923 has fallen into the public domain! Some people, such as Jack Valenti and Mary Bono, have urged Congress to extend copyright to forever less one day.¹ This is far, far beyond reasonable. Our society is a human institution. And as such, "limited times" should be viewed from a human perspective. Lengthy and repeated copyright extensions undermine the spirit of the Constitution, and ignore human reality: we die. Limited times that extend beyond our own lives are useless, nothing more than a token gesture. Until corporations and government officials understand that they're dealing with human beings, they will continue to experience failure here.
What is the solution?
First of all, we encourage movie goers to take advantage of the movie industry's guilt-trip trailers: make their platform your soapbox. Boo their ads right in the theater, or shout "respect the public domain!" Don't underestimate the influence even a quick quip can have on a theater full of people getting lectured in the dark.
Second, send an email to your Senator and Representative. What would you write? I would copy most of this letter, rewriting certain parts to be sure that it reflected my personal views.
Third, blog. Seriously. Get the word out. Write something compelling, and keep doing it.
And finally, consider releasing your own creations under founder's copyright. It's a stopgap measure, but at this point, the U.S. government hasn't given its citizens a sane alternative.
¹ The official Library of Congress URL to Mary Bono's comments changes daily, apparently. So I linked to a relevant article. But should you wish to read her comments in full, try this: go to the Copyright Term Extension Act page, scroll down and click on the link, "Mrs. BONO."