I wonder what counts as an "emergency" and "cyber attack" and what is the extent of a "portion"?

These terms seem too vague for me, take this example: Someone tweets that Obama has killed a baby kitten, Obama could shut down Twitter because it's an emergency, he was falsely accused. He could shut down Facebook too, and all services that could be connected to Twitter to stop this cyber attack from spreading.

No disrespect, but I seriously doubt that the majority of the people(not just Americans) actually know how the Internet works, it's like asking a first graders to solve a differential equations.

The Internet just works fine by itself it does not need supervision from the US government, in fact it is one of the reasons it works so well.