It is his inalienable right to not sign a loyalty oath. He is (was) free to chose a career that does not require affirming one's dedication to all principles of our Constitutional Republic and economic system. He benefited from our system and in returned he provided much entertainment.
As a member of the teaching profession however he would not have had the inalienable rights to indoctrinate students, IMO. Students have inalienable rights too as do the parents paying the bills.
Amen. For that matter, the campuses are full of leftist students who spend all their time protesting, We should make them sign loyalty oaths or kick them out of school.