I don't like 'Monopoly' because most people don't recognize that as a fundamental problem. In fact in the case of media, monopoly is assumed as necessary to provide you with what you want (hundred million dollar blockbuster films).

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.