This is a very leading question. "Piracy" is immoral within the context of copyright. But if the copyright system itself is immoral (because, for example, the successful enforcement of copyright is in total conflict with important digital freedoms), then we should get rid of copyright. Or maybe reduce it in some way. In which case the term "piracy" will lose meaning, and we will just call it "copying".
The context I'm considering is one in which copyright itself may be justifiable. In such a case, it's still possible to create "copyright" laws that don't actually serve these justifiable purposes.
For example, let's pretend that everyone agrees on the following: A country which produces no art is bad, and we should therefore protect incentives for people to produce it. It wouldn't immediately follow that digital piracy is unethical, unless it could be shown that it destroys incentives to produce music.
So you're not asking the question "What are the strongest moral arguments against piracy?", you're asking the question "What are the strongest moral arguments against piracy, if we all pretend to agree that a country which produces no art is bad, and we should therefore protect incentives for people to produce it?"
Firstly, that's a lot of assumptions to make, and to anyone who disagrees with them, any further discussion may be uninteresting.
Secondly, the assumptions are somewhat confused or ambiguous. "A country which produces no art is bad". What do you mean by "bad"? (And is there ever going to be any circumstance where a "country" never produces any art at all?) And what precisely do you mean by "art"? "We should therefore protect incentives?" Protect which "incentives"? Incentives provided by copyright laws as they exist right now? Natural incentives, like "I like painting"? Incentives like "200,000,000 people downloaded my art on the internet, which makes me happy to know they they all like my art, even though no one paid me"?
And if we can decide which incentives it is that need protecting, and that we _should_ protect them, are we agreed on _how_ we are going to protect them, or to what lengths we should go to protect them?
Conclusion: we will need to spend a lot of time discussing the premises of the question before we ever get to the point of answering the question itself.
You're right, of course, but I don't think a deep dive into the premises is a practical. There's just not enough time. Any high level discussion is going to require the participants to many layers of premises.
Whether we like it or not, there are basic beliefs about copyright already entrenched in American culture and law. And even that is based on a common sentiment regarding property and ownership. Which can't be justified without a shared belief in having a government in the first place. Etc. I could keep going.
Instead of starting from the bottom up, or from some arbitrary point in the middle, I think a top-down approach is more practical. As messy as it is, that's how the law has to work, otherwise decisions can never be made. Let's just take the status quo for granted, and ask: "Are recently-passed and newly-proposed laws even consistent with the primary goals of copyright?" Or, to frame it ethically instead of legally: "Does digital file-sharing conflict with the societal values that led us to value copyright in the first place?
I suppose it's necessary to clarify exactly what those societal values are. But, from a practical standpoint (not a theoretical one), it would be premature to begin debating the justification behind the values themselves.
