A clearer understanding of what is ultimately problematic in the SSPX position comes from Saint Francis de Sales in The Catholic Controversy.

St Francis dismantles the Calvinist claim to an “extraordinary mission” apart from the ordinary authority of the Church. His argument is simple but devastating: if anyone can declare a “state of necessity” sufficient to justify ministry without lawful mission, then visible unity and ecclesial authority begin to collapse.

That cuts uncomfortably close to the SSPX argument!!

Just like the SSPX, the Reformers also claimed: • the hierarchy was corrupt • the faith was endangered • extraordinary measures were necessary

Of course the SSPX are not Protestants. They preserve Catholic doctrine, sacraments & apostolic succession. But the ecclesiological principle St Francis warns against still applies: who objectively determines the existence and limits of “necessity”? If the answer becomes “we do”, then the Church risks moving from visible authority to self-authenticated mission. That is precisely the danger St Francis de Sales saw in the Reformers.