Opus Dei creates legally vulnerable adults i.e. "adults at risk"
In the UK, the modern term for vulnerable adults e.g. the mentally disabled, elderly with serious dementia, is "adults at risk". In general, the legal protections afforded minors are extended too to adults at risk. Courts can hear applications to make decisions on their behalf in their best interests.
I would argue that any adult, no matter how intelligent or competent, becomes an "adult at risk" in practice as soon as they fall victim to a cult like Opus Dei. Their freedom and consent is very quickly nullified by the heavy emotional pressure to conform to a mentally exhausting array of religious practices, with major social consequences for non-compliance.
Diagnosing psychological vulnerability
Obviously the difficulty lies in diagnosing a psychological vulnerability serious enough that the state and medical professionals need to be involved in protecting that adult from themselves. That can happen when a person is legally and forcibly sectioned (UK term) or committed (US term) to a psychiatric facility or when there is a sudden collapse and the family get involved, like in the Catherine Tissier case - see https://docs.google.com/document/d/1DZStzLYzzn9UCbkHu533Xm4wyBrtBjoxztN9INyMO5E/edit?tab=t.0
A psychiatrist could then give an opinion that there was an association between Opus Dei abuses and the symptoms. In the Tissier legal case, a cult expert was also heard by the court and their evidence accepted that Catherine's Opus Dei environment was coercive.
The difficulties in using a diagnosis
However, it may then be difficult to make use of such a diagnosis, especially if the adult recovers and chooses to lie low or even go back to Opus Dei (though Opus Dei leaders have a reputation for offloading psychiatrically problematic members).
The diagnosis also may not help establish a case that the adult was known to be vulnerable by Opus Dei at the time of recruitment or up until the collapse. And this is also the problem many years later, when a person has sufficiently recovered from Opus Dei-trauma - which takes many years - to take steps to seek justice. They may be able to get a psychological opinion that they were an adult at risk while in Opus Dei, but legally that may not fix Opus Dei leaders and entities with actual or constructive knowledge of this.
It is in such loopholes that cults like Opus Dei continue to flourish, or at least survive, resting their shaky structures on the fundamental freedom of religious liberty, a liberty they abuse to remove others' liberty.
A loving pastoral response?
What would be the pastoral response? It would be to ensure that all Catholic groups that are in the business of attracting lifelong vocations, Opus Dei foremost, are required to pay for an independent psychiatric assessment of potential members, and regular follow-ups.
Dom Dysmas de Lassus, head of the Carthusian order and author of "Spiritual Abuses in the Religious Life", describes a religious vocation as a kind of extreme sport. What elite sportsperson is not willing to submit to regular check-ups to make sure they are competing and training safely?
Interestingly, such assessments have been mandatory in the discernment process for diocesan priests in England as far back as the 1980s. Perhaps Opus Dei leaders, in the run-up to that group's centenary, could learn from them, 40 odd years later. Or perhaps there are conclusions that bishops could draw from Opus Dei's unwillingness for the last 40 years to reach the same conclusion as they did, that love means safeguarding vulnerable people from major spiritual commitments.