Seeing the good
> university education probably isn't a public good
Well, that kinda depends on the subject being studied.
We can probably agree that most degree courses these days involve adequately educated 18 year-olds leaving home (much to their parents' relief) and going off to study a subject they like, think they'll like or were coerced into by their secondary school's in a bid to improve their ratings. Most of those who survive the parties, house-sharing dramas, love affairs, exams and occasional spot of intellectual striving will soon be moving back in with their parents (if they didn't move house at the first opportunity and "forget" to mention that to their offspring), when they realise their qualification is no help whatsoever in putting food on the table, or paying the rent.
However, some degrees for some students result in "goods" so far beyond the average, mode or median (choose whatever statistical measure you like), that they are undeniably a public good. Take as an example any technological advance over the past 60 years. Almost all have been made by degree-educated individuals and would not have been made if they hadn't received their tertiary education.
Obviously, there is no way to predict which particular student(s) in which particular course(s) will go one to invent or discover something that will change the world. But we can say, that for certain types of course: lets call them "sciences", the more people who study them at a sufficiently high level, the more discoveries and inventions will benefit the world as a whole. Though the same probably can't be said for economics students.
Therefore it follows that for the world as a whole, it is a sound investment to promote, grow and even pay for these sorts of courses: the ones that as a numbers-game do create things that make our world better, safer, more prosperous and nicer. As over time, we will want, use and even need the stuff these people will go one to give us. Patents or no patents.