At the moment a lot of people seem to have trouble engaging with reality, and that seems to be caused by relatively small disinformation campaigns and viral rumours. How much worse could it get when there's a vast number of realistic-sounding news articles appearing, accompanied by realistic AI-generated photos and videos?
And that might not even be the biggest problem. If these things can be generated automatically and easily, it's going to be very easy to dismiss real information as fake. The labelling of real news as "fake news" phenomenon is going to get bigger.
It's going to be more work to distinguish what is real from what is fake. If it's possible to find articles supporting any position and a suspicion that any contrary new is then a lot of people are going to find it easier to just believe what they prefer to believe... even more than they do now.
[1] made-up number, but doesn't feel far off.