It's not just the individual graduate who benefits from their education, the entirety of society does. The most obvious benefits are economic in nature, but one certainly shouldn't underestimate the non-economic side-effects of a highly-educated populace.

I'm certainly happy for my tax money to be spent on funding education for everyone, to as high a level as is useful to them; furthermore I have no objection to people learning less practical subjects, as long as they learn something. And if a more vocational route suits some people better than a traditional academic one, then they should be allowed to do that too. There are many far less useful things that our tax money gets spent on, at least education provides a decent return on the investment.