- It's unnecessary (who came up with the idea that primary education lasts for 12 years, anyways?). I dropped out of high school 2 years early to go to an early entrance program at the University of Washington with 34 other students. And you know what? Very few of them felt that they were academically missing out on anything from high school. The strongest concerns students have about early entrance were (a) social life and (b) not being able to apply for top universities. I think entering college 2-4 years early should be an option for a significant fraction (~5%) of HS students, as many of us agree that we aren't even that academically exceptional.
- It's an extremely artificial environment that constrains your imagination of what's possible in the world. High school socializes you to do well in high school, but it doesn't prepare you well for the real world afterwards, where you realize that creating value for other people really is the most important thing, rather than signalling that you're the smartest/most desirable person in the room. There are so many college graduates who feel completely lost in their life not knowing what to do (and deep in debt), and I think if they had the opportunity to take a gap year (or two) just to unschool themselves and to talk to a diverse range of other people, then they would gain a lot of knowledge about what's possible, and the things that work for them and those that don't. This would, in turn, help them make better decisions about their future while they're still young.
See Danielle Fong's Bio for an example of the amazing things you can do by dropping out early.
Or as Paul Graham eloquently says (What You'll Wish You'd Known )..
If I were back in high school and someone asked about my plans, I'd say that my first priority was to learn what the options were. You don't need to be in a rush to choose your life's work. What you need to do is discover what you like. You have to work on stuff you like if you want to be good at what you do