I think it's unrealistic to expect the majority of 16-18 year olds have any idea what they want to do.
I thought I wanted to be a journalist, but actually upon doing it for a few months, I quit. And I'll never consider it as a career path again.
I still don't know what I want to do, which is why unspecialised degrees are good and essential to an economy. As they display to potential employers a number of skills, one of which being common to all would be an ability to work to a very high level of scholarship.
The opposite would be a system in which all degrees were specialised, which is fine for the few students who are sure in what they wish to do for a career and will do it until retirement. But forcing all students into taking specialised degrees could lead to a number of graduates deciding upon entering employment that they have made a mistake in their chosen career path. And holding such a definate and atypical degree, they may find great difficulty in finding another job that offers the same pay-scale, and thusly, have difficulty in paying off their Student Loan. Obviously, this could cost a government an almost unfathomable amount of money.
This issue is pretty close to the OT too, since the tuition fee rises and education cuts have made a number of universities consider downsizing their tutoring in humanities.