Is your concern that recipients would think it's real? Or is it that people will get an email/chat message containing NSFW material? (because the latter happens now, and is nothing more than background noise at most). What is your actual, specific concern? (genuinely, I have no idea, but want to try to understand - to me it feels like panic about a problem that isn't actually a real problem).
But I think there's a difference between a crud photoshop picture that a person has on their PC, and a (more or less) convincing deepfake video of a person being broadcast.
I think you're likely right that there is an element of panic. I don't know a lot about Korean culture, but I imagine the concern is that deepfakes can have real-life negative impact on people's lives, either because people think it's real or because it creates a hyper-sexualised social environment that endangers women. Both are worthy of concern in my view.
There's still no case for why fake video is apparently so much worse than fake images. Both achieve the same effects when sent maliciously to a relative or contacts list.
I'll (try to) steelman the case for why video's worse: because people don't realise how easy fake videos are to make. But in 1-2 years... meh... most of society will have it figured out.