What's more scary than fake sex tapes is the potential for easy plausible deniability for real criminality.
If they're not and they're hoarded by tech companies or intelligence agencies then we'll just have a lopsided system where people aren't aware of how capable such technologies are, what their limitations are, how to analyze them to spot issues, etc.
Imagine if only nationstates knew about these sorts of technologies and used them for war or if only certain elites in tech had access to them and used them to implicate competitors in crimes? The technology is out there now - at this point, public knowledge is our best defense - people always question if a contentious image is photoshopped, we want that same level of questioning to happen for videos.
In terms of this being used as an excuse to get someone out a criminal charge, it might make us take a better look at the chain of custody on video evidence but I don't think it would invalidate it completely.
This might seem nice against ever growing CCTV, but probably state security cameras will be "trustworthy" and all media evidence gathered by private persons will be dismissed...
The potential for manipulation is huge given how many people trust pictures. I know that I don't distrust most pictures I see.
What GP is describing is the long term consequence of not being able to trust video evidence. Now even if you film someone red handed, they can deny it.
Another dire consequence is that the entire archive of all videos filmed since the beginning are now tainted by doubt. Any past politician speech, any past horror caught on film, etc. can now be said to have been crafted recently.