I don't think copyright is totally bad. For example, I recently published my first novel. Without copyright law, someone else could grab my novel and start printing/selling their own copies of it. I'd wind up competing with my own novel. Then there are issues of film studios being able to take anyone's work and make movies based off of it without compensating the author at all. I'd have to spend a lot of time and money filing lawsuits to make them stop and, without copyright law, I might not be successful.
The big problem with copyright law isn't its existence. It's the length. Copyright was originally 14 years plus a one-time 14 year extension. This isn't so bad. The novel I just published would have until 2044 (assuming I renewed the copyright) to make me money. Then, the book transfers to the public domain for others to build on it. Very few works still make money after 28 years - and I'd wager most of the ones that still do (like Star Wars) partly keep making money because of new material being added.
However, over the years, copyright terms lengthened until now it's 70 years after the author's death. If I die at age 90, my novel will be protected by copyright until 2135. At that point, my youngest son (now 9) would be 128 - and likely deceased. If my youngest son had a child at 30, his child would be 98 when my copyright ran out. I don't need copyrights on my works lasting until my great-great-great grandchildren are born. That's not giving me incentive to create new works. 14 years + 14 years would be plenty.
If copyright law was reset back to 14 years plus an optional one-time 14 year extension, a lot of the problems with copyright would go away.
Nice analysis, but...
Corporations are effectively immortal, and are being imbued with the legal rights once reserved for humans. Well, at least in the US anyway, thanks to recent court cases like Citizens United and Hobby Lobby. Not sure about the rest of the planet, but I'm certain the success of American corporations in getting legislation passed to favor their interests (or prevent legislation inimical to their interests, see below) is not lost upon the business communities in Europe and Asia.
As it stands, copyright law was written long before the rise of corporations and their political influence. It was created in an environment where people had a very finite window to create and profit from a work, as your cogent analysis makes clear. If a corporation is effectively immortal, though, then this underlying assumption about finite windows is no longer valid. Existing copyright law would need to change to reflect the fact that corporate copyright holders are not constrained by the same finite windows that humans are. Lo and behold, that is exactly what is happening, via laws enacted to extend the length of time the copyright can be invoked.
You make very valid points about the copyright period, but your solution doesn't take into account the needs of corporations, who have a vested interest diametrically opposed to your solution. Any attempt to roll back the current time limits on copyright would be resisted by corporate copyright holders who would stand to lose hundreds of billions, if not trillions of dollars of potential profit. Corporate copyright holders would act to preserve the status quo, and would prevent any such legislation from ever seeing the light of day. Again, I can't speak for Europe and Asia, but it is certainly clear that the interests of corporate copyright holders in America are already well-represented in Congress -- that kind of legislation wouldn't even get out of committee, let alone make it to the floor for a vote.