This is the crux of the problem and it goes beyond the ability to determine fact from fiction. Yes, it’s horrible that video evidence in court will likely be indeterminable but the bigger problem, imo, is that it will provide even more endless opportunity for people to believe whatever the hell they want and for bad actors to prey on it.
We’ve already experienced people existing in alternate realities based on tampered video and pictures. As an example, Trump wholeheartedly believing a literal “MS13” was tattooed on that guy’s fingers when it was just a cheaply photoshopped version of what the symbols stood for. Now apply AI and make that impossible to debunk and you’ll have endless people being manipulated and happily having any reality they want verified to their satisfaction. It’s already impossible to reach these people with truth and it will only get worse. There are bad actors lined up for miles waiting to further manipulate people. They won’t have a prayer to suss it out for themselves.
It’s much worse than an “unfortunate byproduct”, it’s basically the end of any fact based reality.