Megan McArdle* has a particularly long post about file-sharing and the entire notion of property rights. It's worth a read, because it does a pretty good job of summing up why all those justifications you have about downloading free shit are still morally wrong. (Her article veers a little bit too much into parallel hypotheticals, but if you can get past that it's worth it.)
While this doesn't directly tie in to SOPA, it's certainly related--since that awful, horrible piece of legislation was crafted to stop this sort of abuse. And, in a way, I think this is a call to action for those opposed to SOPA to come up with a valid alternative--or else convince everyone the status quo (or something close to it) works just fine.
Unfortunately most proponents of file-sharing are absolutists about it, and can't get past the fact that if you download a copy of something, you are still depriving someone of money (or the potential for money) even if they still own a copy of it. If you grab a copy of, say, Hangover 2, would you ever pay for it? Absolutists would come up with some BS about how they would never have bought it at the price it was being offered for, and if they truly thought it was worth it they would buy it, which everyone who was born on the planet Earth knows is a complete and utter lie. The reality is that the intellectual property holder of the work has the right to sell it at whatever price they wish--and if you don't like the price, you don't get it. There is no constitutional right to get free movies, music, and books.
That said, a case can certainly be made that our IP laws need reformed. I honestly don't know enough about it, but it seems like the young creative generation has somehow managed to come up with ways to work within the existing legal framework (i.e., Creative Commons). Does copyright need to be reigned in by the behemoth Disney? Probably. Should the rules about trademark protection be relaxed so companies don't have to behave like dicks and send cease and desist orders all the time? Sure. But the core of IP law is fundamentally sound, in that since IP can't be treated like a material good, it has to have special rules; and those rules protect the creator while also allowing consumers some freedom to enjoy it.**
The pro-SOPA crowd wants to beat a fly with a sledge hammer, forcing everyone to bascially not be creative at all in the first place lest they get taken down. Likewise, anti-SOPA zealots who consider all IP a form of theft also destroy creativity, since no one would ever be compensated for their work. Simply opposing it can't work; proposing something that protects creators while not using the draconian power of the law is the only realistic outcome.
*I swear, I will stop linking to her articles, eventually, but I haven't found anyone else who 1) write so much in depth about the exact sort of things I'm interested in and 2) does so so frequently.
**Personally, I would like to see some sort of specific IP-led reform, where actual specific works run out of copyright after a reasonably short time--say, 25 or 30 years--while the characters/world/plot of a work is still held by the holder (perhaps at the current rate of death of creator+70). In other words, as an example, Star Wars would have run out of copyright in 2007, but the creators would still retain the rights to the Star Wars characters, world, etc. Anyone could then buy or watch the actual movie Star Wars, but no one could make a new Star Wars movie without the creators' permission. Unfortunately, this would upend a lot of current law, so I don't think it is workable, but it seems the best of both worlds.