Intellectual Property is the philosophy that thoughts, ideas, sounds, sights, etc. are owned by the person who first conceived/made them. Intellectual property is non-physical including, but is not limited to: musical, literary, and artistic works, discoveries, inventions, and words, phrases, symbols, and designs.
The aforementioned intangible objects are protected under copyrights, trademarks, patents, and more.
Infringements on copyrights are often, considered stealing, partially due to propaganda spread by video marketing companies, like this video:
The Christian's (and the movie's) main argument against "piracy" that it "is stealing". If I go to wal-mart, take a CD and run out with out paying, I am stealing the CD. If I torrent the data from the CD, then I am not taking a tangible object, therefore I am not stealing. If I paint a picture, and someone takes it from my house, they're stealing. If they takes a photograph of it, and then they print it, they are not stealing.
The Christian's second argument is sometimes "A worker is worthy of his wages." Just because I paint a picture that is, to my perspective, very beautimous, does not mean that I am entitled to someone's buying it. If someone does buy it though, it belongs to them.
And if you are and atheist or the like, then I don't see why you would have any conscience issues doing anything, because you have little reason to be "moral", except the government's laws and social peer pressure.
I am not saying that you should "pirate" whatever. I am stating the belief that intellectual property is bogus, and "pirating" is not theft.