When I was in college over 60 years ago I had a Marxist professor say exactly the same thing, “Not everyone is entitled to their own opinion.” It is dogma on the left.
Herbert Marcuse.
Right in the Wiki, thats where your prof got it. If it was 60 years ago he was cutting edge.
“Liberating tolerance, then, would mean intolerance against movements from the Right and toleration of movements from the Left.
Surely, no government can be expected to foster its own subversion, but in a democracy such a right is vested in the people (i.e. in the majority of the people). This means that the ways should not be blocked on which a subversive majority could develop, and if they are blocked by organized repression and indoctrination, their reopening may require apparently undemocratic means. They would include the withdrawal of toleration of speech and assembly from groups and movements which promote aggressive policies, armament, chauvinism, discrimination on the grounds of race and religion, or which oppose the extension of public services, social security, medical care, etc.”