This isn’t an axiom. It’s just Karl Popper’s opinion. One of the few times the paradox of intolerance was actually invoked in a legal setting was in Communist Party of Germany v. the Federal Republic of Germany

The German federal government had petitioned for the Communist Party to be banned in 1952 on the basis that the party's revolutionary practice means "the impairment or the abolition of the fundamental liberal democratic order in the Federal Republic". Following hearings, the Federal Constitutional Court ordered in 1956 that the party be dissolved and its assets confiscated, and banned the creation of substitute organizations.