Just a couple things, frequently home schoolers have a support network. they can participate in group functions with other homeschoolers. The area I live in has a group of about 20 that meet once a week, and participate in labs, and gym class activities.
These networks will also pool the talents of the parents, and some parents will do class lessons at a shared facility or a community center. So, if there is physics major as a parent, they can teach a class of homeschoolers. If there is a carpenter, you can have shop class.
Concerning extra curricular activities, the parents are still paying taxes, and there are many cases where homeschoolers can participate in high school sports. There was a successful NFL player the was home schooled, though his names escapes me. Played DE for the dolphins, and was an allstar.
Concerning socialization, public schools can be a negative. Many homeschoolers will be cultured shocked at college, but do adjust over time.
I also feel that schools and those people who set up curriculum's and standards should take the trend, and take the current public education system to task to improve public education, because right now it sucks, and homeschoolers are excelling.