The anti-SOPA crowd argues that this is a matter of basic liberty. But it's not. In a free society, you don't have the freedom to steal your neighbor's property. And that should include intellectual property. Moreover, it is the function of the state to enforce those rights. We don't leave it up to civil litigation to protect property rights (although that is part of the solution). We give the state substantial powers to stop theft. Just as owners of tangible personal property have good cause to call for a police force and a system of criminal courts, owners of intellectual property have good cause to ask the state to stop those who would infringe on their rights.
This is an important economic issue for the United States. We are large producers of intellectual property: movies, novels, software, video games, TV shows, and even economics textbooks. If offshore websites find a way to distribute this intellectual property without paying for it, it is as if organized crime were stealing merchandise from a manufacturing firm at the loading dock. It is neither efficient nor equitable.
Maybe SOPA goes too far. As I said, I am not knowledgeable enough about the details to judge. But we need something along these lines. Believers in free enterprise, property rights, and economic liberty should be among the most vocal advocates of laws to stop intellectual piracy.