A long time ago, there was a concept that you were ‘innocent until proven guilty’. SOPA, on the other hand, assumes you are guilty and can shut down your favorite web site before the owner of the site has been alerted of the infringing content. Not to mention the owner is now liable for the content that some user innocuously posted.
The piracy acts could do this, and could make sites like Wikipedia, YouTube, and Facebook many times slower (say goodbye to realtime updates) and more expensive as reviewing everything posted requires extensive man power.
What happened to the freedom in the U.S.? The government is going to increase in size to manage DNS blockades? It will step in and add regulation to the internet similar to Australia with an easily achievable abuse that would silence free speech similar to the great firewall of China.
To scare you of China some more, consider that church web sites, their videos, and their musicians are some of the most likely to accidentally use copyrighted material.
For what it’s worth, some of the DMCA works. Violations were reported and YouTube and other major (and minor) sites took down content. Isps dropped violating customers, effectively doing what SOPA intends.
The DMCA is not without abuse either. YouTube and Megaupload megavideos have been publicized as receiving many complaints, but in the end, much of the content was original – or even uploaded by the claimant or its subsidiaries – with SOPA, instead of a hit video being blocked for a few hours while it is investigated (and losing revenue) the entirety of YouTube could be DNS black listed.