Imagine you are a shop owner and someone writes something offensive on the outside of your building without you even knowing about it. This bill would allow the government to shutdown your store before you even knew the writing existed.
Today we already have in place a mechanism to notify the store owner, but SOPA changes that. It makes it possible to shut down entrepenuers, the store owners and wealth creators on the internet, before they even have a chance to get started helping to revitalize the American economy.
"But how would you not notice someone graffitied your wall?"
I dig this analogy: http://news.ycombinator.com/item?id=3426990
I was picturing an outside wall with the shop owner inside all day behind the counter. The Mickey Mouse one is more concise though.