It seems that there are more and more people whom you hear about homeschooling their children. I must say I have the utmost respect for people who can make that decision and make it work. I was an education major briefly in college - and teaching isn't my thing. And I know you don't have to be a certified teacher to teach your own children, but beyond that, I have reasons for sending my children off to the local public school every morning.
First, I think it is important for children to experience different personalities and points of view from their teachers. Every adult brings with them the experiences of their lives and can provide fresh insight into a variety of things.
Second, there seems to me to be as much value in learning the lessons of how to get along with difficult classmates or teachers as their is in any social studies or math lesson. That's different than getting along with a sibling.
Third, when homeschooling I would imagine it would be very easy to give into the child's individual wants and desires at any given time. "I don't want to do math now" "Okay, we'll do English". (I don't homeschool, I'm guessing how it could be, I might be wrong, perhaps people manage to keep very strict schedules, I don't think I could.) But, that's not always the way life works. Sometimes you have to do math even when you're not in the mood. Better to learn that now, than on your first job.
Fourth, my daughter and I can both be very bullheaded. If I tried to teach her all her lessons we'd probably kill each other. Better for her to be upset with a teacher and vent to me. If she was upset with me - where could she vent?
Fifth, I do teach my children at home. They may go to the school for several hours a day - but every hour that they are with me they are learning from me. Maybe it is learning how to cook dinner, or how to be honest by returning the extra change the cashier hands me. Maybe it's how to help out a friend, or investigate a subject they are interested in. They are always learning from me. But for math, science, reading and social studies, they go to that big brick building half a mile away.