Agreed.
Though actually, Eliezer used similar phrasing regarding Richard Loosemore and got downvoted for it (not just by me). Admittedly, “persistent troll” is less extreme than “permanent idiot,” but even so, the statement could be phrased to be more useful.
I’d suggest, “We’ve presented similar arguments to [person] already, and [he or she] remained unconvinced. Ponder carefully before deciding to spend much time arguing with [him or her].”
Not only is it less offensive this way, it does a better job of explaining itself. (Note: the “ponder carefully” section is quoting Eliezer; that part of his post was fine.)
Having just listened to much of the Ethical Injunctions sequence (as a podcast courtesy of George Thomas), I’m not so sure about this one. There are reasons for serious, competent people to follow ethical rules, even when they need to get things done in the real world.
Ethics aren’t quite the same as tradition and protocol, but even so, sometimes all three of those things exist for good reasons.