Soundslike one of those rules to make the job of the tribunals less onerous.
The problem with the exception was recognized early after, if not before, the promulgation of the code in 1983, and the Holy See introduced a wide consultation with bishops and canonical faculties about it that lasted a number of years before the declaration was issued. It certainly does help.
Unless prohibited by Divine law, Marriage in another faith tradition would be valid, without being subject to Catholic Canon Law.
It’s a little broader than that since canon 11 would continue to apply: Merely ecclesiastical laws bind those who have been baptized in the Catholic Church or received into it, possess the sufficient use of reason and, unless the law expressly provides otherwise, have completed seven years of age.
The law excepts the formally defected Catholic only from three things: the requirement of the form of marriage which is imposed for validity (c. 1117), the requirement for permission for licit mixed marriage to a baptized non Catholic (c. 1124), and the invalidating impediment of disparity of cult (c. 1086 §1).
But it does not exempt them from the rest of the law. Those who have formally defected according to the terms in the PCILT declaration remain subject to other matrimonial law of the Church. Consequently the impediments of ecclesiastical law would continue to apply even if a formally defected Catholic wed in another faith tradition. For example, even if the civil state would permit a first cousin marriage, canon 1091, § 2 would still render such a marriage invalid unless dispensed (consanguinity in the 4th degree of the collateral line).
I believe that the act of formally joining another Christian Community is a formal act of leaving the Catholic faith.
In a particular case it certainly might, but it might also just represent the notorious rejection mentioned in canon 1071 and elsewhere though. Since the law (and the declaration) distinguishes between the two (defection and rejection), we must also.
The will (or intention), knowledge, and legal capacity of the person are critical. The third component to establishing the act of formal defection is that a competent Church authority has to receive it. (Some readers might think “formally joining” as a going through those rituals or actions by who one joins another religious body. One problem is that “formal act” has one meaning here in the canonical sense and what “formally joining” means for the other religious body and the person would have to be examined.) Any individual case would need examination.
One can also defect by a formal act without adhering to another Christian Church or ecclesial community or a non Christian religious body in any way whatsoever. The two notions — leaving and joining— are separable actions. One can simply defect just as one can also commit heresy or schism, rejecting doctrine or rejecting governance, without joining any other religious body. (See the part in the PCILT declaration about the removal of one’s name from government religion registries for civil effects. This issue was partly behind the declaration as I understand it. But again, removal did not require joining an alternative.)
Then too, we also have this interesting issue. Infants or minors might be brought to another Christian Church or ecclesial community or a non Christian religious body in such a way simply because they are under the control of their parents or guardians. It may be questionable that a minor has the capacity to place such an act, and highly unlikely that an infant can place an act of the will with juridic effect.
What is helpful for me to think about is that here the Church, while not sanctioning the defection in any way, wishes to let the person exercise the divine natural right to contract marriage validity in these situations, so it removes the ecclesiastical obstacle in them. The defection would be lamentable enough, and the Church does not wish to compound it in regard to marriage.
