We already use the metric system when it suits us. The 2011 Ford Mustang has a 3.7 liter engine, we get the electric bill in kilowatt hours, and my second favorite rifle shoots a 5.56 millimeter round. For decades every American school child has learned the metric system alongside US customary units, and who will argue that having both has made our doctors or scientists less cutting edge?
I personally believe it will always be 90 feet to first, the neighbor borrowing a cup of sugar, and pick up a gallon of milk on the way home, dear, but the fact that we use a different system for certain things doesn't imply that we can't or don't know how to use the metric system.
There are also benefits in having two systems. I'm reminded of a story I heard about a manager who used to keep an abacus on his desk. During meetings, he'd do calculations on the abacus, knowing that there was very little risk of anyone else understanding the results. Having lived overseas I can attest to the value of being able to describe dimensions in a way that only certain people are likely to understand.
Moreover, when have Americans ever accepted that any system was best just because the rest of the world was using it? Our experiment in democracy went from a collection of backwater colonies to the imminent world super power in a blink of the historical eye precisely because we do not accept that what the rest of the world does is necessarily the best way to do things.
We're the only industrialized nation that uses our measurement system? So what? We also don't have a parliament or prime minister, but that hasn't kept us from being a major player in international politics .
Argument from popularity is a logical fallacy and recognizing that is at the heart of American greatness.