Let's be honest, some schools are better than others. Some teachers are also better than others. Not every county in the United States has an overflowing budget and therefore can only afford the basics in regard to education. Additionally, some schools are extremely rough and are merely institutions to keep kids off the streets during the day time, and in doing so, don't actually invest in the level of educational rigor that other schools do. Private schooling, along with homeschooling, provide parents with the ability to make the choice of which education would work best for their children.
I don't think its necessary to invest in private school unless your district sucks. If you live in the city and your schools are not the best, than maybe invest in it. I go to private school, only because the schools in my area aren't the best. But if they were better, I would do public school