This writer, based on his experience as a tennis guru, seems to have helpful intentions (he argues against homeschooling budding tennis pros), but it's obvious he's not familiar with homeschoolers who are talented athletes and who have mastered the art of playing hard and expending energy into something(s) other than their sport.
For instance, Tim Tebow, the Florida Gator's QB, was a solid student, memorized Scripture, and worked in an orphanage in the Philippines during his homeschool heyday. But even as a BMOC,* he still does volunteer work.
Tennisista Browne, regrettably, does manage to lose his compassion (altho it's hardly the first time this peculiar survival of the fittest argument has been made): "Kids need formal schooling for an abundance of reasons ... Students must deal with the class bullies and other factors that can distract from learning."
He should take a look at Purdue's study about gifted children and bullying. Distressing and depressing.