There is no moral argument for piracy.

There are all sorts of moral arguments against big media. There are all sorts of moral arguments for peer-to-peer sharing of content as beneficial to the artists. But there are no simple, trite, clear-cut methods for arguing that failing to pay royalties for the personal use of media is not the same thing as depriving the rights holder their rightful royalty payment.

Piracy is often the outcome of a costs/benefits mismatch, however. A black-or-gray market for something will develop when the consensus holds that something costs far more than it's worth. We're now arguing consensus, though, not morality... which, after all, trails consensus. It used to be immoral to kiss a person of another race. It used to be immoral to have sex outside of marriage.

Thoreau argued that if you disagreed with a law you should break it, but you should also be willing (eager, in fact) to pay the penalty for breaking that law. The penalty for piracy is often nothing. If you get caught, it's whatever you can negotiate. Hey - stick to private trackers and never get a notice? You're morally within the law, at least as far as the guy who wrote Civil Disobedience is concerned.