Let's see.
For starters, Yeongsaegyeo is
not a generally accepted part of christianity. It's also different from the Yeongsaenggyeo which kidnapped and murdered a bunch of people half a century ago. It's basically a cult with a leadership of two, Choi's father was the first head of the religion and Choi is pointed to be the second, and the cult was founded in 1970.
(sidenote: it's incorrect to say that any old religion founded back then could be seen as radical, because Christianity came in much earlier. According to Wikipedia which cites a book <Kenneth Scott Latourette, Christianity in a Revolutionary Age: Vol. 5: The Twentieth century outside Europe (1962) pp 414-5> the "Catholic population [was] reaching 147,000, and the Protestants 168,000 in the mid-1930s." Since the two religions kept growing, any religion founded in 1970 can only be seen as a cult both in terms of radicalness, numbers and canon. Forgive me for not actually reading the citation, I'm not writing a paper for class here so... <effort>)This is an ad for Yeongsaegyeo. It says something about "the savior the Creator has sent us will teach you the three values from the three religions: Buddhist nirvana, Protestant Holy Spirit, and the Catholic Heaven" and also says that you can cure any disease and uch at the bottom, and urges you to come to this one place. It's quite obviously not Christianity, because Christianity in general abhors other religions and by definition focuses on Jesus, not a random dude, as the savior. It also calls god "God," "Lord," "Father" more often than the Creator.
Now, mind control and whatnot are farfetched, but it's definitely true that Choi has had a large effect on Park. 100% of her speeches were edited by someone with no experience in speechwriting and no relationship to the government. And tons of governmental reports (which are confidential to civilians) were delivered to Choi, circumventing protection laws and programs. Correct me if I'm wrong, but normally how lobbying works is the president mentions "oh hey there's this policy that might hurt you" and the other guy says "yeah, it would suck" and then the president nudges the policy in a different direction that benefits the other guy. I suppose people see Choi as more blatant and unforgivable corruption. In this case it seems that Choi was delivered daily governmental reports, commented on the policies and recommended ways forward for Park, and on top of that edited all of her speeches despite not being a speechwriter or in any way connected to the government.
Addendum: crimes that Choi and/or Park and/or her underlings are possibly committing
Choi & Blue House officials: Violating confidentiality of military secrets
Choi: Exploring and acquiring military secrets
BHO: Leaking national secrets
BHO: Leaking diplomatic secrets
BHO: Leaking executive secrets
Choi & BHO: Offending the Law on Presidential Report Handling
Choi: Accepting/inciting bribery
Certain political defenders of Park: Brokering of bribery (ie, accepting a bribe from A on behalf of B, then giving it to B)
Varios benefactors of the nonprofit: Embezzlement
All benefactors: Embezzlement & Misappropriation of non-profit funds for personal gain
So half of these charges are related to national law and the other are plain old corruption.
here are my sources, unfortunately they are all in korean
Hangyeorae website line to line comparison of Dredsen Speech, which I used to verify that at least for this speech the meaning wans't radically changed.
Namu wiki page: Choi Sun Shil Gate overview of "choi sun-shil gate." It's not Wikipedia but rather Namu Wiki, which works on the same wiki base but has a much larger number of participating people. Korean wikipedia is kindof a shell compared to the English one.
Namu wiki page: Choi Sun Shil this page emphasizes that Yeongsaegyeo is NOT Yeongsaenggyeo.
Kukmin Ilbo (Citizens' News) article this news article reiterates that fact and is also the source of the advertisement. Incidentally, Citizens' News is a Christian-founded media so it may be biased, though the newspaper advertisement seems to be legitimate.
PS: You might note that my tone is a lot more neutral than before. This isn't goalpost moving I swear ;-; I'm just changing my opinion based on more research. My new stance is that while the Choi corruption case is not a fantasy case of mind control, it still is looking likely to be manipulation (since they have 30 years of history) by Choi... and if you look just at the facts, it's a pretty serious crime to have someone leak important documents to a private source that is not secure at all,
plus have that same source also edit all your speeches,
plus have Park directly funnel funds to a non-profit rather than mildly change policy to have the same effect.
PPS: I do think that it's not logical to call bloody murder for direct corruption (literally channeling money to someone else) over indirect corruption (aka lobbying, or changing policies and laws to have the same effect). But it seems more personal this way I suppose. I guess a lot of the disgust also comes from Choi being part of a self-proclaimed cult rather than a traditional religion.
Also, there is direct evidence that all these things happened which helps fuel the flames.
PPPS: I tried to make my thought process as coherent as possible but i don't think i did a good job, just look at these three post-scripts. Welp.