Is there some downside of that to you? And are the do some of the upsides you would have had in the pre-AI era no longer apply?

Yes - previously there was some chance someone reading the ideas on the blog would contact the author to thank them, or ask them to collaborate.

When laundered via LLMs whose pretraining destroys all credit, that can't happen.

he's missing out on any attention that his shared thoughts would bring? and all benefits that might bring if he's good at what he does.

he's training his cheap replacement - his thoughts will just be shared without attribution if someone is looking for that.

The downside, as stated in the message, is implicitly supporting the LLM data ingestation pipeline by providing fresh content. It's not a direct harm in itself, but feels very tragedy of the commonsy