If a person doesn't break any pre-existing laws, then they must not suffer any legal consequences, sure. And nobody is suggesting that Page and Brin should spend a minute in court or pay a cent in fines.

But a corporation isn't a person, it's a business instrument, and if the United States were to judge that the existence of that instrument is detrimental to the greater security / stability / welfare of the nation as a whole, they would have every right to write a new law to ban usage of that instrument, i.e. ban the existence of Google in its current form, as they once wrote a new law to ban the existence of the United Aircraft and Transport Corporation.

In the past we've taken a harder stance on giants like this and as a matter of precedence we can do it again.