Even though this is ULTRA creepy, I don't think the US government would ever shut down any big US website. How much tax money does Facebook pays ? Now you understand that actually using this legislation against US business (which have, obviously, US websites), is like shooting yourself in the foot for the US government. But of course this isn't a reason to accept such a ridiculous law. It is basically infringing like the whole constitution, especially with the privacy and the innocence presumption parts. And even though a court would never shut down big, mainstream sites like youtube, it could shut down more subversive ones, heavily threatening freedom of speech.
If the law ever passes, the first thing I expect is a sudden increase in server uptime price outside of the US. What makes a website "american" ? The servers or the company ? Either way, goodbye american internet startups, hello to all the clones from around the world. And what if they ban the DNS entries for all those "rogue" sites ? Lol... that's what Lybia did. Not long before the old man was killed.