Isn't it enough to teach people how to properly perform unit conversions (then show them the cell phone app)?
Within the context of science education, it is a much easier to focus on understanding the mathematical relationships which underpin theory using metric. Use of customary units (US or UK) will result in more students falling back on the use of memorized magic numbers and not proper derived constants. Understanding concepts of scale in science becomes an order more difficult as well.
For this reason, metric units (mks or sometimes cgs) units are by far dominant in scientific papers and texts. Imperial has some presence in engineering, possibly due to a more narrow focus and more resistance to change.