It is of course possible that it might (eventually) be convincing enough that no human can tell, which would be problematic because it would suggest human speech is indistinguishable from a knee jerk response that doesn't require that you communicate any useful information.
Things would be quite different if an AI could interpret new information and form opinions, but even if GPT could be extended to do so, right now it doesn't seem to have the capability to form opinions or ingest new information (beyond a limited short term memory that it can use to have a coherent conversation).
Sounds just like the chess experts from 30 years ago. Their belief at the time was that computers were good at tactical chess, but had no idea how to make a plan. And Go would be impossible for computers, due to the branching factor. Humans would always be better, because they could plan.
GPT (or a future successor) might not be able to have "an internal point of view". But it might not matter.
If an AI were to make it impossible to make a living doing programming, would that be an improvement for most readers of this site?