If you post a ridiculous quote, say it’s from Obama, then provide a link to a video where Obama says that quote, more people believe you. People already believe tabloid journalism. Just because you might exclusively trust NYTimes doesn’t mean easily accessible mechanisms for fabricating evidence aren’t a problem for a massive chunk of the world population.
And what about when this happens at a state-sponsored level (This is absolutely already in development, if it hasn’t happened already...). “Did you see that Fox News exclusive video leaked from the Bernie Sanders campaign? Yeah he was holding a private dinner for a bunch of Billionaires. They say they got it from some Russian oligarch he invited. So much for grass roots change, I think I’ll just stay home this Election Day.” Or the corollary: “That smoking-gun tape the Do-Nothing Dems have of me at Putin’s personal sex trafficking center, where the two of us are laughing about having Epstein take the hit? Fake news! They’re called deepfakes, and they make these just absolutely incredible fake videos. Not real at all though. Only trust what the Government-sanctioned media says!”
As per your other point, given the GANs that are used to make these are precisely a deep fake AI fooling a deep fake detection AI, aren’t we already there? Further, when the government is making the generator, a privately trained discriminator has no chance. How would you even train that? Get the government to give you a bunch of generated fake media so that you can develop a really spot-on model? I don’t think so.
Two predictions:
Deepfakes will play a roll in the 2020 election.
Deepfakes will play a roll in every election thereafter.
If this doesn’t concern you, I don’t know what would. The thing with the “post-truth world” is that once people think we’re in it, we are.