Dowling v. United States
The Grokster case affirms that unlawful copying is as much a crime as theft is, but it carefully avoids calling it theft. Mainly because the Supreme Court already said that copyright infringement was not theft.
Doesn't make it legal, ethical, or moral; but it's not theft.
Well, while it may not be theft in strict legal terms, Congress passed the NET act, or No Electronic Theft act, which was passed after the referenced case as follows.
NET Act: 17 U.S.C. and 18 U.S.C. as amended (redlined)
So, if congress titles the bill with theft, the president signs it, even if it's not technically "theft", from what I see, our government equates the severity of copyright infringement as equal to or a type of theft.