A couple of points that don't appear to be addressed so far:
1) The existence of a copyright doesn't keep anyone from playing, performing, or otherwise using the copyrighted material. It does mean that when they do so in a commercial venue, they have an obligation to pay the appropriate royalty. How much the total royalty is depends on the parties involved in the copyrighted material, but as I recall, the composer/author's royalty is something on the order of 12 cents per use. So far as live performances and the playing of recorded music in restaurants and similar venues are concerned, the author is never going to collect more than a tiny fraction of the royalties due, so they're largely irrelevant. And anyway, these uses were scaled back in the most recent legislation: the extension of copyright dates was a trade-off for more free usage of material. There are also quite a few exceptions to copyright--circumstances where royalties need not be paid.
2)Many songwriters make (or hope to make) their living from their music. I don't see anything wrong or selfish about this, do you? Very few songwriters amass millions to pass down to their heirs: the vast majority just struggle along, and their copyrights may well be all they have to leave. I don't think allowing children to benefit from their parents' creative work is unreasonable. They will only benefit to the extent the work remains (or becomes) popular: and if it IS popular, you can bet that SOMEONE is going to make money off it. Shorter copyright periods will not make recordings, sheet music, etc. any cheaper to purchase: they'll just cut the songwriter and his/her heirs out of the loop.
3)One of the best things, from a songwriter's point of view, about new technology--including the Internet--is that it makes it cheaper and easier to release independent recordings and to publicize the work of independent musicians. Now, I'm sure one motivation for longer copyrights on the part of large music corporations is to make sure they continue to make money off music they already own, in case more and more musicians and writers go the do-it-yourself route, or refuse to tie themselves into long-term contracts. Instead of attacking the author's copyright, why not support independent music? That would show that your opposition is genuinely to corporate control of the music world, as opposed to simply feeling you have the right to something (another person's original music) for nothing.
4) I can't see how extending copyright would "stifle creativity". Are you suggesting that no one would write or publish any new songs if they could continue to make money off the old ones? It just doesn't work that way: our culture always wants something new, or a new version at least. However, not being able to collect royalties for their work could sure stifle a lot of creative people, at least to the extent that they'd have to spend most of their time making a living at something else.
5) Finally, I have to say I was shocked to see the overwhelming opposition to copyright extension on this site. I'm fairly new to Mudcat, but I thought its focus was traditional music and, to a lesser extent, contemporary singer/songwriters. You've got centuries of music already in the public domain available to you: why do you begrudge those of us who drive from town to town playing $50 bar gigs, or work in offices during the day and try to write and play open mics at night--and keep hoping we might someday actually see a royalty check with more than three digits--because we prefer not to give our work away?
Just for the record, yes, I'm a singer/songwriter; I have a day job--and it ain't in the music industry; and so far I haven't collected a penny in royalties. But I'm still hoping.