> If it becomes so good to be completely indistinguishable from reality, then not sure what the gripe is.

Being 100% convincing doesn't make it true. Not being able to tell what's true from what's fake is a self-evident problem. It means you're at risk of forming an invalid view of the world. The only safe approach would be to never believe anything, at which point we've even lost recent history. Madness lies that way.