The founders believed in the principle that once an idea is shared, even if it's simply one person relating a story to another, the second person has a copy of the idea in his head, and that both people now "own" the idea. That person can then share the idea with others, and that ideas, whether they be musical, artistic, pure science, or engineering should be shared - and in fact could not be owned. That society and one's ideas are built on the foundations of the ideas that came before them.
They also recognized that if an author, engineer, or what have you couldn't make money off of his ideas, he was much less likely to bother to create them in the first place, or if he did create them, he'd do it in the guise of trade secrets that would never become part of the public domain, or private showings in the case of copyright. If an idea isn't shared, the public domain doesn't grow, and advances in the sciences can actually regress because an individual or corporation never shared how to create something.
To encourage works to eventually enter the public domain patents and copyrights were created, granting the author a monopoly of the distribution of his works for a limited time to gain a return on his works. In return, when that time expired his ideas would be available, for free, to everybody. The government makes sure of this by keeping a copy of the registered copyright or patent.
I'm perfectly willing to argue the benefits of a much reduced copyright term, and to explicit DMCA exemptions to allow fair use. That playing the radio at a restaurant doesn't equate to a live performance, and that the adds on the radio are sufficient payment for the rights to play the radio at a work premises. The copyright term could be as little as the founder's 14 years. I believe life of the author OR 25 years, whichever is longer, is equitable, but the term of the copyright could certainly be expanded or contracted. I have no problem with copyright being longer than patents as a patent generally will be used in the creation of other things, while the copyright is very specific and only protects a very specific work.
What I'm not willing to grant is that anything that's ever been written or produced is free game for everybody to download, gratis, the moment the work is published. Even if I were willing to grant this, and lawmakers embraced it, I doubt that freeloaders would get what they wanted. Quality works of art, music, video games, and other media, as well as inventions, take a TON of work. Not as a hobby. Not as something to be done for fun outside of your "real" job or just for the love of it, but AS your real job, and more often as the real job of a whole host of people.
I think a ton of people would stop producing media, or do it in such a fashion that the media becomes much more exclusive. Live concerts only, no pressed CDs, for instance. "Yeah, that's the way it should be man!" Never mind the guy saying this might have gigs of downloaded, studio produced CDs. Forget the PC unless the game requires a net connection. We're into console games only, or games where all the content is run off of some centralized servers and you have to pay to get access to said content. A lot of the applied sciences would dry up as corporations become even more cliquish, hording all of their secrets, rather than protecting them for 25 years - or hording them more than they currently do. And, no, I don't think killing off whole industries or types of content so that we can all get everything for free is healthy. It won't be free, and it'll be MUCH more encumbered than what we currently have.
Unfortunately there's not a great way to stop piracy, but there are ways to limit it. Having a convenient way - ala iTunes, Steam, or other popular digital distribution channel - to get ones work is one way, especially if it's more convenient and safer than torrents or rapidshare. Careful pricing is another. NOT ticking off the paying customers with adds against piracy - that the pirates will simply remove anyway - that the paying customers are forced to sit through, pissing us off at the works' owners. International sales are trickier. The same price DOES NOT work across national boundaries, and things that are legal in one country can get you into a lot of hot water in another. I also think that the going price for punishing copyright infringement is pretty silly. It should be like a speeding ticket. $25 per work or something. Sure, if you've terrabytes of media you're sharing, that's still enough to bankrupt you, but I won't argue that that isn't fair if you're illegally sharing that much work.
I think the life plus 70 of copyright is ridiculous. I don't think there's a viable alternative to copyright out there. I think if everybody pirated works, and only paid for those works that they liked the very, very most, or thought that the author was indie enough to deserve a buck, if you remember it after you're done playing his work or listening to his music, but before you spend your money on beer, that there wouldn't be the plethora of content out there that there is today. I think there's a middle ground somewhere out there between the MPAA/RIAA regime and the yokels who argue that somebody who spends months or years of his life - or the lives of a whole team - don't deserve recompense for their efforts, or only deserves recompense on the freeloader's terms, and that this middle ground will be fought over and revisited time and again, and that the fight's healthy, even if some of the laws that emerge from it definitely aren't...and that run on sentences rule!