If I had to paint in broad, evocative strokes, I'd claim the industries are using the government to prop up their outdated business models by destroying competition from users.
So I'd suggest 'Monopoly.'
The key thing to focus on is the imbalance of power SOPA creates and how that will end up getting in the way of Uncle Art's evening entertainment. So far the shoplifting shutting down the store analogy is the most pointed I've heard, but still not a catch phrase.
My hope with the term 'Prohibition' is to turn it around and put the focus on the evil being done by the media companies. They want the government take away your rights, because they don't want to compete fair and square with web technologies.
Here's an analogy I've been using that might work: "They're tying your hands behind your back so you have to pay them to feed you."
"They want the Government to create a Prohibition so they can have a Monopoly on content"
That said, I do think 'Prohibition' is an accurate description. SOPA may well be the first step in a 'War on Piracy' that does have strong parallels with '20s prohibition and the drug war. SOPA is a futile attempt to stop normal human behavior - sharing of content. It won't work. The fact that it won't work could lead to even more draconian blocking measures, creating a self-reinforcing loop of ever-escalating restrictions and punishments. 'Prohibition' conveys that futility and extremeness pretty well for a single term.