Exactly, I think it's a problem only if it leads to lower "engagement" by humans. I kinda doubt it will. Most reading and writing that occurs on the Web, by a large margin, is already very low-value, not noticeably better than a near-future "AI" will very likely be able to produce.

If ad impressions & clicks don't drop, Google, FB, and others won't give a shit where the content's coming from. If impressions & clicks go up (not an unlikely outcome, I'd say) they'll even encourage it.