Obvious point number one: The adjustment process that brings the US external deficit down could be smooth, or not-so-smooth.   We don't know. 

No country as big as the US has run a deficit this large for a sustained period of time off an export base as small as that of the US. New York Federal Reserve President Geithner: 

"The plausible outcomes range from the gradual and benign to the more precipitous and damaging"

Obvious point number two: Even if modern financial technology and greater cross-border capital flows allow "greater dispersion" of current account deficits and surpluses globally, a US trade and transfers deficit of 7% is not sustainable forever.