You're right about that, but why take chances when if you teach your child yourself, you can be assured that your child will get a good education? Even the good schools have some teachers who are bad.
I started homeschooling 15 years ago and my kids are doing very well in college, high school, middle school and elementary school. The first time my kids end up with teachers that I haven't screened first is when they start taking college courses. In those cases, they're old enough to not be indoctrinated and they've acquired the proper learning skills to be able to learn class material when they get a lousy professor. And believe me, that has already happened several times. Thankfully, they've learned how to learn and are not at a disadvantage when this happens.
That assumes every parent would make a good teacher :-) But it's a valid point.
I'm a fan of private schools, personally. I spent all but one of my junior high and high school years in private school. I live in DC, and there is a whole host of good private schools around here. Now, if only we could get the city government to agree to vouchers. Surprisingly, the mayor here seems to be in favor of tenatative steps in that direction.
Pretty much anything would be better than DC public schools. They spend around $13K per student, with disturbingly poor results. There is a street that runs along the border of DC and Maryland. Houses on the North (Maryland) side cost about $100K more, due to the fact that they're in the (excellent) Montgomery County school system.