The unemployment among college graduates is 2.6%. So there is actually a shortage of college graduates in the workforce rather than a surplus. And when people are more educated, they are more productive (common sense, but it can be empirically demonstrated, too), which confers broader benefits in the economy. If we have more college graduates, we'll have more companies trying to take advantage of that fact, etc.
That's kind of nuts, though. We have no shortage of people to work low-level jobs, and only 30% of Americans over 25 years old are college graduates. We'd benefit from trying to bring that number up. We can worry about any problems that come from overshooting our goals when we're within 50 years of reaching them.
That would indeed be a good thing, though by that time, we probably won't have sanitation workers.