Asimov published four books in 1980: Casebook of the Black Widowers, How Did We Find Out About Oil?, In Joy Still Felt: The Autobiography of Isaac Asimov, 1954–1978 and How Did We Find Out About Coal?
Of those, Casebook of the Black Widowers was a collection of mystery short stories and the “How Did We Find Out About” books were childrens’ non-fiction, which leaves only In Joy Still Felt as a potential candidate for this quote. I downloaded an EPUB version of this book and did a search for “libertarians” and found nothing.
Either the OP got the year wrong, or they just pulled this quote out of their ass.