I would guess that people who believe in government conspiracies has low or even very low trust of the government. Give them an story that display that the government can't be trusted and people will attach themselves to the narritive in order to confirm how they feelt. They don't need to try hard to actually rationalize it, because the actually details are unimportant. The only thing that matters is the feeling of confirmation.
It is really hard to convince people out of a feeling by using facts and proofs, and a common statement during online discussion is that it is impossible.
I agree with this. I think the problem with deepfakes is that they could make it impossible rather than "really hard" to "convince people out of a feeling by using facts and proofs." Not only will those people have "a feeling" to back up their false beliefs, but they'll also have convincing fake "facts and proofs."
Those fake "facts and proofs" will also make it easier to convince others of the false beliefs. With deepfakes, it could be possible to convince someone with moderate to high "trust of government" of false government conspiracies (e.g. a convincing high-resolution deepfake showing Hillary Clinton knowingly engaging in child sex trafficking or talking about adrenochrome).
> I might go as far as to say: "Deepfakes aren't a huge concern because we live in a post-factual society, so evidence doesn't really matter."
Deepfakes are concerning because they point to a future where disinformation is so effective that it's impossible to pierce a disinformation bubble and unreasonably difficult for a sensible person to avoid getting pulled into one.
Take the idea that the moon landings are a hoax. It relies on accepting the idea of a rather unbelievable and expensive (for the 60s) amount of fakery. Sure, people believe it anyway, but they have to try pretty hard. They wouldn't have to try so hard if someone had faked a convincing body of evidence that the landings were faked. Or they'd have to throw up their hands and give up if they understood how easily things could be faked with modern technology.