One anecdote given the 'PR' worries raised:

I have never read the sequences. After reading Luke's post, I am much less likely to: the impression given is the sequences are generally idiosyncratic takes which recapitulate an already existing and better organized literature. I also think it is more likely the sequences are overrated, either through readers being unaware their (or similar) insights have already been made, or lacking the technical background to critique them.

It also downgraded my estimate of the value of EY's work. Although I was pretty sceptical, I knew there was at least some chance that the sequences really were bursting with new insights and that LW really was streets ahead of mainstream academia. This now seems much less likely - although I don't think EY is a plagiarist, it seems most of the sequences aren't breaking new ground, but summarizing/unwittingly recapitulating insights that have already been made and taken further elsewhere.

So I can see the motivation for EY to defend that their originality: his stock goes down if the sequences are neat summaries but nothing that new rather than bursting with new and important insights, and EY's stock is important for things like donations, public perception of him and the SI, etc. (Both my likelihood of donating and my regard for SI has been lowered a bit by this post and comments). However, EY's way of responding to (weakly implied) criticism with catty arrogance compounds the harm.