And the benefit to society of a person (who eventually waits tables) getting an education (which wasn't about how to wait tables) doesn't need to be manifested while that person brings you your check. That person has a whole life outside of work where they can benefit from a richer understanding of the world.
As an example, we're a (kinda) democratic society, and a lot of the sanity of our government and policy rests on the judgment of the citizenry. Dealing with political rhetoric, forming opinions about sometimes highly technical public policy issues, and understanding economic policy at a minimum require an ability to critically evaluate rhetoric, some level of scientific literacy, and some numeracy, which are all benefited by a well rounded undergrad program. In some places, the political process requires that people not only be able to follow and evaluate political platforms, but produce arguments on their own (I'm thinking of state primary caucuses in particular). Having an educated populace is important independent of the desire of individuals to be wealthy or professionally successful. Just because we need waiters and parking lot attendants and bar tenders doesn't mean education is wasted on the portion of the population which fills that need.
If your concern is with public funds subsidizing education, I would actually have greater objection to funding educations for people that go on to earn high salaries in jobs that require high levels of education -- those are students who could afford to take loans and pay them back.