I should add that this anti-prostitution flash-mob seems, to me at least, to come very close to political advocacy, something that is illegal for foreigners according to the laws concerning immigration.
Yeah: this. Forget Yegob's antagonism for a minute, please. I'd personally recommend anyone on an E2 visa or working in the public school system
not to get involved with stuff like this. Encourage your Korean friends, sure, but don't get involved personally. Also bear in mind these political neutrality rules apply to
all public school teachers. It is not explicitly in my contract as far as I recall simply because that'd be redundant (as immigration law has it covered), but it is in the Korean ones I believe. As such, in the eyes of the public, you'd essentially be crossing this boundary not once but twice if you're with EPIK.
This specific case is borderline political maybe, but this isn't something you want to risk. Besides, a foreigner protesting a local issue in Korea is, if anything, going to sway public opinion the wrong way
no matter what that local issue may be.