Why is the Metric System better?

In America we use the English System of measurement, which is kind of funny, because even the English don't use it anymore.

    1. So what is the Metric System (System International FRENCH)?
    2. Why does the rest of the world use it?
& 3. Why is it better for science?

The following TEDed Video helps to explain?

So what do you think, should America join the rest of the world? (Our scientists already have).