If you are fully attentive, you can correct course once you realize a mistake is being made. My Honda Civic has adaptive cruise control and lane keep, and I run into issues with it reasonably often. I'm not complaining: after all, it's not marketed as much more than glorified cruise control. And either way, turning it on is not a risk to me. With any of these features, in my opinion, the main risk is complacency. If they work well enough most of the time, you can definitely get a false sense of security. Of course, based on some of the experiences people have had with FSD, I'm surprised anyone is able to get a false sense of security at all with it, but I assume mileages vary.

Now if the car failed in such a way that you couldn't disengage FSD, THAT would be a serious, catastrophic problem... but as far as I know, that's not really an issue here. (If that were an issue, obviously, it would be cause to have the whole damn car recalled.)

All of this to say, I think we can leave the guy alone for sharing his anecdote. When properly attentive, it shouldn't be particularly dangerous.