The basic size of metric units was arbitrarily determined is what he means. It's not that multiples of 10 is a bad idea, it's that the basic sizes just don't "feel" right.
"It's not that multiples of 10 is a bad idea, it's that the basic sizes just don't "feel" right."
Which is only because we have grown up and been educated in a society that uses the far-more-convoluted English system.
The metric system is more logical and easier to understand; however, I'm more familiar with the English version and thus ignorantly prefer it.