This is a misconception. None of these social situations are unique to a school environment. It can be argued that you can actually increase the opportunities for social engagement outside of the confines of school.
seems to me like school is the great melting pot of our society,
now that I'm out of school it seems like I live a very Bowling Alone (http://www.amazon.com/Bowling-Alone-Collapse-American-Commun...) existence, I interact with people at work, and family, it seems like that is the exent of my non superficial interactions
maybe I'm paticularly introverted, but I wouldn't home/unschool my daughter simply because I don't want her social universe to be that small
also schooling is one of the few shared experiences in our society
Having had chicken pox is an experience most of the population also shares. Now I contracted the virus as a baby when my brother brought it home from kindergarten. Can't say as I remember it at all as I was barely out of the womb, but I apparently got so few pox marks that I got shingles as a 20-year-old college senior, and oh what fun that was. Has our son had Chicken Pox? No, as we opted to get him the vaccine. I hope he doesn't feel we wronged him by depriving him of a typical childhood experience.
When our son was 5 and homeschooled, he was playing in the ocean while his traditionally educated cousins were in school. My brother asked me, "When are you going to let him out into the real world?"
My response was something like this:
"If you think your children are in the real world because they are in a traditional school, I think you are deluding yourself. Do you have to ask permission to urinate? No, and neither do most people in the real world, but your children do. Ditto getting a drink of water. Are your children starving? No? Well, that is the real world for many children (as of 2010, the the United Nations Food and Agriculture Organization puts the figure at over 13% of the world population is undernourished, but I didn't have an iPhone to look this up on the beach back in 1996). Have your children been sexually molested? Perhaps you'd like to set them up for that experience as it's one many have had."
I gave some other examples of what "the real world" is for other people in the world and ended with:
"I believe we can make our own worlds to a good degree, and feel it irresponsible not to realize that and choose what world you'd like for yourself and your loved ones and to work toward living in that world."