At this stage, these AI's can only help. Imagine we are given this tool that can generate samples from the "uninformative but realistic looking text" distribution, we can then put it in a discriminator to filter out blabbering bots and humans together, or invert it to summarize the small kernel of information, and that would be a great thing. The better these models learn about typical human behavior the better off we are at identifying the truly exceptional. It's when AI starts to sense and incorporate novel information from the non-human environment that you really have to worry.
Perhaps, but that's the world we live in. I suspect the average reddit commenter is already more articulate than the average person (citation needed, I know. But reddit skews highly educated young male in a first-world country. There's no way they do worse than a worldwide average).
Other than that, I agree with your comment.
But it's no symbolic reasoning. It's not constructing a counter-argument from your argument. It simply lives off previous epic rap battles of internet flamewar history about .. well, about anything, since it's the Internet, and people like to chat, talk, write essays on every topic there is. Satire too. So there is always something to build that lang model on.
Though that will come too. Eventually.
Conjecture: GPT-2 trained on reddit comments could pass a "comment turing test", where the average person couldn't distinguish whether a comment is bot or human with better than, say, 60% accuracy.