The most common question I and other homeschoolers get is, "how is your kid going to learn to socialize?" or "How will he have enough of a social life?"
It's pretty funny that most people instinctively know that the most important thing about going to school isn't LEARNING - it's socializing! Anyway.
The thing about school is that it actually helps create anti-social behavior. For instance, it creates "peer-centered" children, who can't look adults in the eye and who are obsessed with being accepted by one another. A great book on this topic is Hold On To Your Kids by Neufeld and Mate. I was horrified to see how much "peer orientation" affected me when I read The Diary of Anne Frank (on my own, in my post-graduate unschooling years!) and then referred back to my own diary from the age of fourteen. It was horrifying. While Anne wrote about the meaning of life, family relationships, learning, academics, her place in the world. . . I wrote things like "I wonder if Alex wants to be friends with us" and "______ is bugging me lately." Seriously, these were the most substantive entries of mine. It's because I, like most teenagers in the U.S., could not function until I got my social bearings, which was an ongoing project.
Another thing about school is that it divides kids according to age. So people learn to get along only with people of the same age. In high school, this shifted slightly for my social group, but of course socializing with people from a different class (usually only one year older or one year younger) was really not that different from socializing with people from our own class - except that you're always constantly aware, "Hey, I'm hanging out with the class of '92 tonight." With homeschooling and unschooling, children hang out with people of all ages and are knowledgeable and comfortable with people of all ages. Isn't this a more *useful* type of socialization?
School also breaks up families - kids spend entire days without seeing siblings or parents. This might seem to be better because of "sibling rivalry," etc., but the truth is that there is much less, if any, sibling rivalry in homeschool families, and the parents and kids generally enjoy each other's company. Personally, I had no idea how to get along with my own family when I was little. We so rarely did it. If we were going to spend long stretches of time together, we always all invited friends and broke up our socializing along those lines.
One of my favorite things about unschooling is the cross-generational socializing. My kids spend plenty of time with kids who are much younger and much older, and they don't see any reason why kids who are five or ten years older wouldn't want to play with them. Once they are adults, they are going to have to be working and living alongside people of all ages, so this is an important thing that they won't have to try and learn later. Some people never learn it. In fact, most people I know never socialize with people more than a few years older or younger than them, as adults. It's too bad, because I'd rather hang out with people based on their personalities than their ages.
As far as having socializing opportunities, there are way too many here in the Twin Cities. I can't even figure out how to spend a day *without* socializing. There are so many people that we know, and half of my friends are homeschooling, so there is no shortage of people to hang out with. Besides that there are many Yahoo! homeschool activity groups, many support groups, many "play groups," etc. We participate in a whole bunch of things each month and there is quite a community. Not every area of the world has this, but I think with enough enthusiasm and ambition, something similar could be created anywhere that homeschooling is legal.