Anecdote time: I was not just homeschooled, but unschooled. Unschooling basically means that instead of my parents teaching me, I was expected to learn on my own. They provided some direction and assistance, but they weren't especially well-equipped to teach, and I was always free to choose not to learn something, which I absolutely did do out of laziness sometimes.
I got very into programming, and when I was 18, I launched a Web site which succeeded wildly, and has been paying my bills ever since. I did fine on the SAT, and I had a 4.0 GPA during the year I spent in college. (I left after that to run my company.)
My feelings on unschooling are complicated. Knowing how it turned out, there is no way I would go back in time and make my parents send me to school. But I can easily imagine alternative outcomes where I end up dying in a ditch instead of starting a company. I don't think I would ever unschool a child myself.
But since I'm happy with how unschooling turned out for me, how can I support a law denying those potential benefits to everyone else? That's essentially a law against what caused me to be who I am. I'm fairly certain that if I'd been sent to school, I wouldn't have started my company. It was the result of endless hours of tinkering -- time I wouldn't have had if I'd been busy with homework.
It's a bit like doing a startup versus working a normal job. If you do the startup, you might lose all your cash and fail; but you also have a small chance of winning big. High risk, high reward. The job will give you consistent pay, with no chance of losing your hat; but also with no chance of a big win. Low risk, low reward.
High risk certainly isn't for everyone, but imagine a world where no one ever took risks.