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.