Sure, if he'd come up with this primarly using his own resources and time, but he discovered this whilst being paid to conduct research at a public university, a form of institution which is explicitly intended to disseminate knowledge. Society should enjoy the fruits of its investment.

Would the university have been willing to invest in the exotic printer and the labor to do the work without the potential upside of a patent?

It’s very easy to declare that someone else “should” do a bunch of work and spend a bunch of money for the altruistic benefit of society.