No, college is not all about the diploma. It's about the experience under an academic environment. Your diploma only shows what u did in your major, but you do many other things besides completing your major. Such as living in the dorm, meeting new people, taking elective classes, participating in various groups.
You get to meet many types of people from all kinds of backgrounds, and I believe the social experience provides a great stepping stone to the real world such as a company, or a government agency, where you will meet these kinds of people again.