Don't know if you're still following this thread, but I agree with the responder that the civic structures of society are increasingly replaced by schooling and subscription-based hobbies. I think there are many opportunities to socialize kids without school, but they're not quite as ubiquitous--and they won't become common until lots of people are doing them, like I plan to.
Also, speaking delicately, a lot of poorly-socialized homeschooled children have poorly-socialized parents, and were doomed from the start. I am gregarious and involved in many different social circles (athletics, music, engineering, etc.) and should be able to expose my kids pretty thoroughly to them.