If you're going to allow for some type of training beyond eighth grade, I would agree. Some people aren't crazy about abstract concepts (my dad was one of them), but can build a house from the ground up, wire it, plumb it, and live happily ever after in it.
I'm lousy at building things. Even simple Sauder Furniture bookcases give me the fits. But the Vo-Tech guys I went to school with -- the guys who thought algebra was a type of fancy lettuce -- are master mechanics, furniture craftsmen, electricians, computer hardware specialists, the list goes on.
Everyone needs to learn to read, write, and make change. Beyond that, everyone needs to be directed to training that best suits his or her temperment. Whether the student and his parents choose the 9 - 12 grade curriculum, or the school tests and places the student is another matter for debate. But I do not think high school is optional, not when courses can be designed to fit the student and train him to be a productive 18 year old.
Well, I would ALLOW anybody to try to do anything.
But I would not allow, and I certainly would not require, people to go to school who don't want to be there and who lack the aptitude to succeed.