Total freedom of speech is the most obvious example of the paradox of tolerance.

Fascists rise to power. They silence their critics, corrupt the judiciary and other independent organs of state power.

They are eventually destroyed by liberal forces.

Liberalism then creates a system of free speech, giving all voices equal credence and is tolerant of hate speech.

Fascists use that tolerance to further spread their messaging, eventually leading to the downfall of liberal democracy and a rise of fascist totalitarianism/populist etc etc.