Mostly the military is trying to recruit people who can't readily pay for college upfront these days. That's the real target group I've noticed, because if you can already get into college and pay for it then the military ends up being low on your priorities (like in my case). They're not gonna put a bunch of beheading videos up for "ultra-reality of the middle east", or some sort of "Meet arab women, TODAY!" poster.
Then there's the people who want career experience/leadership experience, which follow along the same general principle.
Edit: Once you turn 18 you're a legal adult as far as the government is concerned so all the fact-finding and research you put into figuring out how you want to spend the next 4 years is up to you really.