He'd often have students come up to him and say they had no idea there was even a case for free markets. All they'd ever heard in school was how awful they were. They'd thank him for opening their eyes.
At one time, the other staff (all socialists) invited him to participate in a debate about free markets in front of the students, and warned my father that they were going to take him apart. He happily agreed.
They wound up rather sorry they'd done that. My father was an experienced debater, and had an encyclopedic knowledge of economics and history. He shredded them :-) and some had the class to come up later and thank him for opening their eyes as well, as they hadn't believed there was a case for free markets either.