While an active JW, I never understood why they were so anti-education. Of course, I was too brainwashed to think about it much. It was simply, "Well, I'm too busy with all of my JW stuff, so I don't really have time for education anyway" and that was pretty much it. Now I see why they are hammering on it so much. Because "education" and the environment surrounding it provide so many exits from the cult.
Like Band mentions, first you might begin to think on your own. That could lead to interpreting the bible on your own, or simply rejecting it as the basis of GB authority.
Then there are those pesky classes, which teach all kinds of things in opposition to literal bible interpretation. Science is a huge one, as is psychology, you might just realize your in a cult!
Then the environment. So many people having discussions which aren't controlled by what is printed in the latest WT. Religious and non-religious people from all over the world, all with different perspectives and interesting points of view. Its just so different from the local KH, no wonder the powers that be don't want you in that kind of environment!
Oh and then there of course is that degree you get at the end. Employers want and need you now, and that will lead to all sorts of problems like having a decent lifestyle with extra money that can be used for things like entertainment and vacation.