Ed Peters has updated his original post on the Chinese episcopal consecrations and has included a new argument. Referencing a Vatican press statement (which unfortunately is only in Italian, it seems), he writes (EXCERPTS):
The comment about bishops and priests being "greatly pressured and threatened" ( I can imagine) to take part in the ordinations raises fresh concerns, I suggest, about their validity. See 1983 CIC 125, etc.
Analogy: Two Catholics free to marry, but under ecclesiastical precept not to marry one another (1983 CIC 1077), and neither of them wanting to marry each other, are forced by government officials to go through a wedding ceremony together. Any guesses as to how many ways such a sacramental "marriage" could be declared null?
This is an argument that deserves to be taken seriously. If you pressure someone to perform a sacrament then you can get them into a state of mind in which they withhold–or are unable to generate–the intention necessary to perform the sacrament. Thus the first canon that Ed links provides that
§1. [A juridic] act placed out of force inflicted on a person from without, which the person was not able to resist in any way, is considered as never to have taken place.
§2. An act placed out of grave fear, unjustly inflicted, or out of malice is valid unless the law provides otherwise. It can be rescinded, however, through the sentence of a judge, either at the instance of the injured party or of the party’s successors in law, or ex officio.
As you can see §1 of this canon provides that completely irresistible force would invalidate (since episcopal consecrations are juridic acts). However, it is not clear that this form of force was used in the Chinese consecrations.
This canon distinguishes in §1 and §2 between force and fear, and some commentators–such as the authors of the Red Code–hold that the former refers only to irresistible physical force. The distinction between the forms of coercion in §1 and §2 would then be that the former deals with physical coercion and the latter with mental coercion.
The green CLSA commentary notes that some commentators regard the force in question only as physical force, though it adds that other commentators think that irresistible coercion of a psychic or chemical nature could also qualify if they sufficiently destroy the subject’s ability to exercise the will such that no human act takes place.
Despite the proximity of these episcopal consecrations to Manchuria, it is not clear that any Manchurian Candidate-like force has been brought to bear on the individuals performing (or receiving) the consecrations and rendered them unable to perform the act validly.
Evidence of such force might emerge in the future, but it has not emerged to date, so far as I know.
We may more safely presume, instead, that the parties acted under fear of the Chinese authorities–and indeed the press statement that Dr. Peters cites refers to pressure and threats, which would seem to indicate fear–thus placing the act under the heading of §2 of the canon.
If that is the case then the law would hold that such an episcopal consecration, "placed out of grave fear, unjustly inflicted, or out of malice is valid unless the law provides otherwise."
Thus in the absence of a canon expressly providing for the invalidity of such consecrations, §2 would lead us to conclude that the consecrations were valid if what was present here was grave fear rather than irresistible force.
(Incidentally, note that this canon expressly speaks of validity if a juridical act is placed out of malice, like the "Stick it to the Catholic Church" motive that the Chinese authorities are presumed to have. They weren’t the ones performing the consecrations–those were performed by bishops–but the canon seems to indicate that even if the bishops themselves had a "Stick it ot the Vatican" motive that the consecrations would be valid, per my previous post.)
It could emerge that a form of invalidating coercion was used in these cases, but until evidence of this emerges–or until another invalidating ground is found–the Church’s presumption would be expressed by the previous canon:
§2. A juridic act placed correctly with respect to its external elements is presumed valid.