But the hierarchical congregation of the SSPX is not part of the hierarchical constitution of the Church. The constitution of the Church consists of lawfully established apostolic or episcopal sees in union with the Apostolic See of Rome. The Society is not an episcopal see at all and it never was. It was founded as a pious union (essentially a lay organization) under the authority of the diocese of Fibourg, but it even lost that status in 1975. So, the SSPX might be a hierarchical congregation, but it is not part of the hierarchical constitution of the Catholic Church. I agree with Matthew that the SSPX vis-a-vis the divine constitution of the Church is no different than the independent Thuc groups.
The SSPX is indeed part of the hierarchical constitution of the Church. It is a "society of the common life without vows". To say that it is essentially a lay organisation, a pious union, is simplistic to say the least. Read the study by the canonist, Fr Glover, here:
https://sspx.org/en/legal-existence-sspxA priest, in order not to be a vagabond and to be permitted to exercise his power of orders, must be incardinated either into a diocese or a religious institute. The SSPX truly falls into the latter category, having been erected in the diocese of Fribourg, praised by Rome, permitted by Rome to open houses in other dioceses in Switzerland and Italy, and allowed to incardinate priests from outside of the Society directly into it.
The suppression of the SSPX in 1975 was unlawful - more properly a criminal affair! - and should not be accepted.
The problem now with the subversion of the SSPX is that both forms of a priest receiving his approval to exercise his power of orders - through the diocesan bishop or through the religious institute - are equally broken, which is basically what Ladislaus and Matthew have been arguing. The sedes, because of their convictions, considered it a broken affair long ago. The supreme shepherd is struck and so the faithful bishops have to assume greater responsibilities to continue the mission of the Church. It is the state of necessity which justifies this law of necessity and ultimately invokes the supreme law of the Church, the salvation of souls. I don't think this is against the constitution of the Church! Whether a bishop erects a religious institute for his priests to work in, or simply "sends" them, giving them a spiritual jurisdiction over souls rather than a territorial one which is not possible, I think it is a judgement for the bishop and not for us... imo...