Except income. The reason people copy protected work is to avoid paying for it.
Property theft is theft, ultimately identical to mugging and shoplifting. It may be an uncomfortable thought but there is no avoiding it.
If I mug or shoplift, once again, they no longer have the money or product I took. If I pirate something, then the original person
still has it. You say "income" is being stolen, but income isn't something you actually
have. It's something
potential. If I decide to not buy something just because I'm not interested in it and never pirate it, then I'm denying you potential income, just like piracy. So the claim it's "ultimately identical" doesn't make much sense, unless someone thinks it's immoral for me to not purchase things just because I don't want them.
Now, there obviously is a difference between simply not buying a product because I have no interest in it versus pirating it, namely the fact that in the latter case I get to use it. But that again means the ethical argument is not the same, because what is being lost is something
potential, not anything you actually
have.
So the argument for it being unethical isn't that anything is actually being taken away, but that something is being denied. And more specifically, that it's wrong to deny income to someone while still making use of their work. So again, the ethical argument is much more akin to that of the question of the morality of paying wages that are seen as unfairly low or not properly compensating someone for their work. And hey, people can criticize that as unethical (comic book companies have gotten criticism for the fact that creators of some of the most popular and lucrative comic book characters saw very little of all of the money the companies made off of them). Indeed, this is what your post really says, that "The reason people copy protected work is to avoid paying for it." Again, since nothing is being taken away (income is potential, not actual), the argument ultimately turns into one of compensation, not of taking. The problem with that in terms of rhetoric, of course, is that what is "unfairly low" wages and what would be proper compensation is much more arguable than outright taking something. It's less rhetorically powerful. The attempt to equate it to mugging or shoplifting seems more of a desire for stronger rhetoric than it being an actual proper analogy.
To be clear, I do think there are frequently moral problems with piracy, and I identified an ethical argument against it above. But I don't think the claim it's ultimately identical to shoplifting or mugging really holds up.
However, here's a question, and I ask it because I am genuinely curious about it. If I get a book, DVD, game, or something else from the library, I'm avoiding paying for it even though I get to use it. No store gets money from me, nor does the original creator. In both cases, income is being "stolen", but very few people would ever claim that it's unethical to get something from the library instead of buying it. There's obviously a legal difference between them, but we're talking ethics here. Unless the argument is that anything illegal is immoral (which carries with it some obvious objections), what is the
moral difference between the two? Obviously, getting something from the library is for several reasons less
convenient. If that is the reason, does it mean that if piracy was less convenient, it would become moral? And if convenience isn't the moral difference, what is?