So at least we have some confirmation from your friend about how controversial the concept of "brainwashing" is in the case of NRMs. My point is: It is dangerous when you solely rely on the brainwashing theory to explain the conversions into NRMs or the existence of these groups. The fact is in the last centuries, NRMs have been flourishing. Why is that? Are people nowadays more stupid or mentally vulnerable to deception? Why do many keep coming to the NRMs instead of traditional and mainstream religions? One day you thrilled the world with the destructive aspect of the Odaeyang or the People Temple, the next day there are ten more NRM groups appeared in the country. What happen to the people of this world? Either they are so stupid and ignorant or the deceptive technique of those religious leaders are god-like. Yet the statistics show that they are not stupid but their majority come from middle and upper classes with good education, and the deception is not that good because only very few percentages stay while the majority leave after some contacts.
But there is another fact that there are so many interested in these NRMs and come to their meetings. It is obvious that they are seeking for something in the NRMs, something which their current religious traditions and relationships cannot provide them. In the documentary of the People Temple, some of the former members confessed about that: they joined because they found there a lively community, a miracle, a self-less way of life, etc. So it seems to me that many people come to the NRMs as active seekers, most of them do not find what they are searching for and leave, but some find (or think so) and stay.
Now, for the few who stay, of course there are un-clear things, but deception and brainwashing are different things. You fall for deception with your free will, and it is very common in life, like advertisements (about a product, a job, a partner, etc.) and reality are usually different. But brainwashing assumes that you can control people's will and thought by external influences. As your friend said, the concept came from the treatment of POWs, many from the Korean War, which included confinement and strict control of total environment. In a larger scale, it requires some total control and closed environment as in the case of North Korea. By this, I do not mean North Korea government successfully brainwashed their people, I just means that the condition for brainwashing is that strict according to its original theory. Such condition is impossible for NRMs, even though they may try to mimic it, especially in the point that people are free to express their different ideas and to leave. That is why the application of the concept of "brainwashing" into cult studies is controversial.
While the argument is still going on whether the "brainwashing" theory is applicable to the few who stay, not the majority who go through the same experience and leave, the imprint of it in common understanding by the work of mass media does have a dangerous aspect: Governments and people stop to ask questions about why those NRMs exist and appear more and more, and why people keep going for them, why not the traditional religions, etc. All these questions are finished with one answer: brainwashing, then no more. And so after they have solved a cultic case only with this approach, more others appear and keep attracting people. The mainstream churches stay hesitant with their conservative traditions, while the NRMs are more sensitive and keep offering people with many attractive things that they are hunger for in today modern life: syncretism between spirituality and science, community of trust, magic and miracle, LGBT, environment pollution, internet, etc. Many NRMs are abused for personal gain, but the reason for their existence and successful conversions and also the lessons we can learn from them are much more than just "brainwashing."
So as long as we take the brainwashing theory as only one approach and aspect beside other approaches and perspectives, and that brainwashing is not the total representation of what NRMs and cults nor their conversions are, I am willing to discuss about it.
PS. About the charge on Mrs. Yoo, if the prosecutors can prove it, then the EBC cannot avoid the question of their relationship with Mr. Yoo anymore. If they deny the connection, then it means they accept that Mr. Yoo and his family illegally used the EBC's money and the image of an innocent, honored Mr. Yoo together with many leaders of the church will collapse. If they admit the connection, then they will either have to face the questions and anger from within or accept that business investments and even frauds are their nature. Or they will have to find someone else to blame, a scapegoat, which I think is almost impossible.