If they only taught metric in school and changed everything else immediately, we would all be comfortable with it inside a year.
If we only taught and spoke English we'd all be comfortable with in inside a year.
It really is unproductive to teach two types of measurements, two languages, etc.
I'll have to disagree with you there. The standard system is basically a hodge-podge of different systems. It has its charms, but it can be rather confusing.