[xfymukod] Constitutional amendment against retroactive copyright extension

I do not see how a retroactive copyright extension "promotes the progress of sciences and the useful arts".  Forward copyright for new works, sure, but retroactively extending copyright isn't going to cause an author, possibly dead by now, to retroactively create more works.

If anything, retroactive copyright extension impedes progress because it prevents new works from building upon old works which will enter into public domain.

Nevertheless, Congress has done this multiple times. No doubt it must have been legally challenged, yet constitutionally upheld.  This suggests a need for a constitutional amendment, prohibiting retroactive copyright extensions.