Actually, you can't really consider piracy as a 'sin'.
Most people would say "Piracy is stealing!", because it's taking something that you haven't payed for.
BUT..here's the kicker: It isn't stealing. Digital material (such as movie rips or mp3/flac) is classified under Copyright law, not under Physical property law.
You should thank our friends at the MPAA and RIAA for lobbying the governments for this distinction. They use this to pretty much avoid paying taxes on the items, as 'legally', they are not considered physical goods.
The best term now is 'Copyright Infringement'. BUT, copyright infringement, in legal terms and in every single court case involving copyright infringement depends on on thing: distribution.
You downloading a song/movie from the net isn't copyright infringement. What is copyright infringement is re-distributing it through a protocol like bit torrent (or selling it on a burned disc)
If you simply download a song from a file locker (me.ga) or usenet, it's a one-way transfer and you're not uploading to anyone else, and therefore, NOT committing copyright infringement.
So, technically and legally, it's not a 'sin', thanks to how Copyright Infringement laws are worded.