Lots of things brought up in this thread do not apply to the topic. Copyright infringement is not an economic issue. Copyright infringement is not a theft issue.
Copyright infringement cannot be meaningfully compared to theft. Theft involves depriving the rightful owner the use of an item. You can't do that with intellectual property, unless one of you know of some mind-erasing technology I don't know about.
Violating copyright is unethical in general for one very simple reason -- the owner of an intellectual property has the right to say how that property is to be used.
When you go to a cinema and sit down in one of its theatres, the only thing that ticket bought you is a license to view the movie one time. That ticket does not give you license to record and redistribute the movie -- hell, it doesn't even give you the license to see the movie twice. So at the moment someone pulls a camcorder out of a backpack and starts recording, he is in violation of license of intellectual property, which is unethical (and illegal). If I download his video, then I am also making use of intellectual property without license -- thus I am behaving unethically (and illegally). You can't argue "but I'm going to go see the movie once it's released in my area" -- the simple act if violation of license is in and of itself unethical (and illegal). You are depriving the owner control of use of the property.
When you purchase a CD, you aren't purchasing music. You are purchasing a limited license to listen to that music. The reason a copy of the music is given to you is that that is the easiest and most portable way to enable you to exercise the license you have purchased. This is why ripping a CD to your own MP3 player is ethical (and legal in most places under "fair use"

-- you are merely applying your license to a modified medium. However, you must have purchased an applicable license to be able to excercise any kind of "fair use" doctrine. Again, arguing "but I'm going to buy the CD tomorrow" also cannot apply -- you listened to the music without license, which is in and of itself an unethical act (and an illegal act in a lot of places).
The are limited circumstances I can see where a violation of a copyright might be if not ethical at least not highly unethical. For example, if you legally use licensed software published by a company that has gone out of business and you require more licenses. If you have in good faith exhaustively tried every effort to obtain more licenses, and if you have failed in your attempts, then I can see copying the software to more machines as possibly being an ethical act. It will still be illegal, though.
Under U.S. law, if I create a work, it is protected by copyright for the rest of my life plus 70 years. If a company is the creator (software, for example), the work is protected for 95 years from first publication or 120 years from creation, which ever is shorter. My copying the software after good-faith efforts does violate copyright law (I'm in the U.S. and assuming a U.S. company).
But my ethical consideration was based on violating a right, not violating the law. I suppose some assets-selloff clearinghouse could have bought the assets of the defunct software company, but what if that purchase only included tangible assets? And suppose the defunct company was an incorporated entity (equivalents [I think]: "proprietary limited" in the U.K. and Australia, "GmBH" in Germany)? The stockholders do not have any ownership of the assets of the company, so they cannot make a direct claim. The programmers can't make a claim at all -- as the company's employees, this would have been a "work for hire".
The copyright will exist for another ~87 years, so my act would be illegal. But whose rights am I violating?
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