Schism is the refusal of submission to the Roman Pontiff or communion with those subject to him. The Society meets both canonical elements even though only one is required for schism.
The Society has refused submission to the Pope's jurisdiction because it has repeatedly reject the Protocol agreements of the Holy See which included accepting the Catholic Church's Profession of Faith (which the Society rejects, like all schismatics). They refuse communion with the Roman Catholic Church which they call the "conciliar church."
The Society also refuses communion with 99% of those in the Roman Rite, because they reject the Novus Ordo.
Those are the canonical elements of the crime of schism. And these elements are proven in the external forum by a notoriety of fact.
But let's face it. Given that Society's theological arguments are so poor and have all been refuted (ask Fr Laisney about our exchanges and challenges to the Society's false understanding of Collegiality which remain unanswered, as just one example), there must be another motivation which keeps them separated from the Church. That, I believe, is financial. Will the Society ever be willing to turn its wealth (real estate, investments, etc) over to the local bishops or Holy See? I don't think so.
As Pope Pius XII teaches in Mystici Corporis, those who are not subject to the Church's divine government are neither living in the Body nor the Spirit of the Catholic Church.
I pray that SSPX priests continue to leave this schism and come into the only ark of salvation, for the salvation of their own souls.
In Christ,
John Salza, J.D , O.P.