Of course I admit that my reluctance to change to metric has more to do with American nationalism than with any sure superiority of our units (although I despise using centimeters for small around-the-house measurements when inches and 1/4, 1/8, and 1/16 inches feel better to me). But at the same time, I think that it is as necessary to have multiple measurement systems as it is to have multiple languages. In the 20th c. especially many people believed that the era of different tongues was coming to an end, but I think that despite the prevalence of English and Chinese around the world, there will always be multiple languages because culture can never be simplified into a single thing. Even in the USA it's possible to go to another region where they use some different words, different phrasings, different ways of thinking, and this is simply a natural occurrence akin to genetic diversity. The more distinct a culture, the more distinct its use of a language, so native English speakers in India do not speak exactly the same English as in the USA or UK. An absolute universal language can never be anything but an artificial construct disconnected from real culture, hence the problem with Esperanto. (And I do recognize that there are some native Esperanto speakers, but that does not remove its failure as a universal, a-cultural language.)
In the end, the U.S. uses the metric system when it's helpful (e.g. in science), and there is no pressing need to switch to it completely. Just because we use the US system doesn't mean that we don't understand the metric system and aren't taught it in schools.