From an indexing/crawling POV, the content generated by LLMs might (and IMO will) permanently defeat spam filters, which would in turn cause Google (and everyone else) to permanently lose the war against spam SEO. That might be an existential threat to the value of the web in general, even as an input (for training and for web search) for LLMs.
LLMs might already be good enough to degrade the benefit of freedom of speech via signal-to-noise ratio (even if you think LLMs are "just convincing BS generators"), so I'm glad the propaganda potential is one of the things the red team were working on before the initial release.
Soon (1-2 years) LLMs will be good enough to improve the general SNR of the web. In fact I think GPT-4 might already be.