Well, you know what they say: with great power...
...comes AWESOME opportunities for abuse.
There's SO much wrong with the whole concept of an internet kill switch. Didn't really help things in Egypt, did it? Probably just made everyone angrier.
And in the US, the internet is a conduit for billions of dollars in annual cash flow for business. Not to mention the business world's reliance on the net for daily operations. I would not want to be the guy who snips that wire.