Thanks for the post. I find myself both agreeing with some of your points, but disagreeing with the way you've chosen to frame the debate:

I agree that:
- theft necessarily deprives the victim of property
- an of act copyright infringement *can* adversely affect the victim
- copyright gives many people an incentive to create art
- some artists support themselves entirely via profits from copyright
I disagree that:
- copyrighted material is the equivalent of property
- copyright infringement *ever* deprives the victim of property
- an act of copyright infringement necessarily affects the victim adversely
- copyright infringement today noticeably harms the progress of the arts

Your view -- that copyrights make an author's work the "property" of that author -- is extremely common. Given the historical evidence, however, I believe that view is completely at odds with the purposes of copyright (in the US, at least). In the words of Thomas Jefferson:

"Inventions then cannot, in nature, be a subject of property. Society may give
an exclusive right to the profits arising from them, as an encouragement to men
to pursue ideas..."

Our copyright laws do not treat words, ideas, thoughts, etc as property that can be owned. They simply give artists exclusive rights to how their creations can be used: copied, sold, displayed, performed, etc. Infringing upon someone's copyrighted work by performing it without permission, for example, is therefore not the same as theft. Even the Supreme Court of the United States agrees: "...interference with copyright does not easily equate with theft, conversion, or fraud."

This technical/legal difference translates into a moral difference, because it necessarily changes the way you view the issue. The Constitution's framers consistently espoused that speech, ideas, and invention should be free, and that copyright is an exception to this freedom. It was created solely to provide incentives for creation, not because it's "morally necessity" to compensate authors. If anything, it was viewed a moral wrong, allowed only because of the incentives it created. More quotes:

"That ideas should freely spread from one to another over the globe, for the
moral and mutual instruction of man, and improvement of his condition, seems to
have been peculiarly and benevolently designed by nature... Society may give an
exclusive right to the profits arising from them, as an encouragement to men to
pursue ideas which may produce utility, but this may or may not be done,
according to the will and convenience of the society, without claim or complaint
from anybody... generally speaking, other nations have thought that these
monopolies produce more embarrassment than advantage to society"
-- Thomas Jefferson

"That, as we enjoy great advantages from the inventions of others, we should be
glad of an opportunity to serve others by any invention of ours; and this we
should do freely and generously."
--Benjamin Franklin

So copyright infringement is certainly not the equivalent of theft. All that said, you may claim that it remains immoral because it decreases artistic incentives, and in doing so hinders the progress of the arts and sciences. If you were to say that, I would agree with you completely. However, today we've expanded the umbrella of what qualifies as an "infringement" much too far.

Original copyright law focused almost exclusively on profits. Works could be shared, read, performed, displayed, etc, as long as it was done in private and for free. Only for-profit public uses of a work required permission from the author. The point was not to force everyone who enjoyed your work to pay, but to ensure that you had a monopoly. In other words, to ensure that no one could compete with you financially. For example, another artist using your work and selling it.

Today, things are different. We have the internet, CD copying, file sharing, etc. These allow people to enjoy share and enjoy artistic works freely and privately. It's not the same as, say, copying 1000 VHS tapes and selling them to passersby on the street.

So when the record labels lobby Congress to make file-sharing illegal, because now they only make $10billion a year instead of $14billion, that's a perversion of copyright law. That's what's immoral. Copyright law doesn't exist to guarantee middlemen insane profits. Nor does it exist to control what citizens do for free in their own homes, whether or not that activity ultimately affects artistic profits. It exists to provide sufficient incentives, and that's it.

The ONLY argument for the immorality of piracy must revolve around whether it is actually harmful to the progress of the arts. My question to you is this: Has the rampant file-sharing made possible by the internet harmed artistic or scientific progress? Are books and movies and plays and inventions disappearing? Is the current state of things unsustainable? Most certainly not. If anything, the opposite is true: sharing on the internet has only spurred the creation of new arts and invention by creating a bigger and more easily-accessible market than has ever existed.

The question can also be presented in reverse: Has the repeated extension of copyright terms, lobbied for by giant content companies, helped the arts? When oure forefathers created copyright law, it lasted a maximum of 28 years. Today it lasts for an entire lifetime PLUS 70 years. Entire decades worth of movies, books, music, etc are being lost, as they remain under the control of copyright owners who have abandoned them because they are no longer profitable. The public could have and would have maintained them and improved upon them. But instead, we have to watch them rot. I'll finish with this quote, from a court case in 1821:

"While one great object was, by holding out a reasonable reward to inventors, and
giving them an exclusive right to their inventions for a limited period, to
stimulate the efforts of genius; the main object was `to promote the progress of
science and useful arts;' and this could be done best, by giving the public at
large a right to make, construct, use, and vend the thing invented, at as early a
period as possible, having a due regard to the rights of the inventor. If an
inventor should be permitted to hold back from the knowledge of the public the
secrets of his invention; if he should for a long period of years retain the
monopoly, and make, and sell his invention publicly, and thus gather the whole
profits of it, relying upon his superior skill and knowledge of the structure;
and then, and then only, when the danger of competition should force him to
secure the exclusive right, he should be allowed to take out a patent, and thus
exclude the public from any farther use than what should be derived under it
during his fourteen years; it would materially retard the progress of science and
the useful arts, and give a premium to those, who should be least prompt to
communicate their discoveries."