He proved that you can blend basketball and an education. There is no law prohibiting players from leaving school early to play professionally, which is too bad. It is done regularly in hockey and baseball. It is occurring more and more in football and basketball. College hoop coaches will tell you that they can't count on more than two years out of their stars.
Football is much the same way.
A prime example is Michael Vick, the first man selected in the NFL draft. Vick played just two college seasons. The second-best scenario is to get the degree as soon as possible. Carter did that and like any college grad, he wanted to be with his graduating class. For his stance, Carter received flack.