The metric system is a much more educationally efficient system than our current system of units. It would help facilitate international communication, and it would mean schoolchildren would not have to waste precious time memorizing arbitrary conversion ratios. In short, it provides a positive externality.
A U.S. metric system transition would be a structured acclimation, in 3-year stages: First, require all non-metric measurements to be accompanied by metric ones. Then, require metric measurements to be featured more prominently. Then, outlaw non-metric measurements. Finally, remove this restriction (for freedom's sake) and allow the USA's metric system to fly like a baby bird.
Potentially, the transition could include a transition to 24-hour clocks.