Its a BS argument used by the teachers union. You can enroll kids in so many different programs (i.e. youth hockey, little league, volunteer service, pee wee football, altar boys if your catholic, etc) that socialization is not even anything like a problem.
I have been a homeschooler all throughout school. There are definitly ways to be social, even in high-home school.
I even went on several homeschool choir trips and went to prom with a girl I knew from the choir. Not to mention the trips to D.C., and other field trips... How often is it that the public schools from GA. take their students to the Chattanooga Aquairium for a field trip??????