> he ends up paying more for the labor, because he is competing in the same labor market as everyone else

You'll have to explain that more. Ship builders aren't competing with plumbers.

>Don't you think spending the working time of 4 million labor hours a year, building megayachts, is perhaps not the most productive/ROI generating activity for society at large

Well, that's a drop in the bucket. But you could apply this reasoning to any form of luxury goods. Where do you draw the line? Nice clothes? Fancy watches? Sports cars? Five-star restaurants? Are any of these "the most productive/ROI generating activity for society at large?" Who decides what goods and services are worthy?

> and perhaps, uh, have _children_

You think people are having fewer children because luxury yachts are being built?