Somewhat inspired by this question, I found this website. To summarize, they imply that they would be legally protected from civil suits from former members who are being disciplined. Would this actually work? My first thought is that it doesn't make sense that a person who leaves cannot revoke their consent, especially since this wasn't a binding contract of any sort.
In Guinn v. Church of Christ, plaintiff withdrew from the church after an internal investigation of her conduct. The church apparently held as a matter of religious doctrine that she must repent of her sins, also that withdrawing from the church is doctrinally impossible. The transgressions were widely publicized within the church; a lawsuit over outrage and invasion of privacy ensued. The upshot of the appeal is that the church can be held liable for post-withdrawal actions, but before that, the church has a privilege to communicate such transgressions (the church is not subject to secular judicature of its actions w.r.t. its members).
Contract law is not relevant here, what matters is that a person can knowingly and intelligently waive their right to litigate against a party, and while one is a member of the church which has such a waiver as part of their disciplinary doctrine, one cannot sue the church for its doctrinary actions as long as the actions do not constitute a threat to public safety which would justify state interference. Although the church argued that church membership is irrevocable, the court found that "Just as freedom to worship is protected by the First Amendment, so also is the liberty to recede from one's religious allegiance". Given that plaintiff had withdrawn consent yet the church subsequently announced the transgressions without her consent, the church was thus found to be liable.
In Stepek v. Doe, the court similarly affirmed that a church enjoys a privilege against charges of defamation, when the plaintiff continues to operate within the church, not having left the church.
So it can "work", to some extent. The person can always withdraw consent; the person has no legal recourse in case consent has not been withdrawn. The article is correct as far as it goes, which is not far enough: it errs in not stating what the legal consequences of of the transgressor leaving the church are.