Do groups include pairs and other smaller unions? I can see the reasoning for thinking that group intentions are progressively rarer in larger groups, but not the reason for thinking that (e.g.) married couples could not have joint intentions.

Congratulations!

Bonus: I give arguments against the orthodox view that instrumental desires are "just" combinations of ultimate desires + means-end beliefs, rather than independent states of mind. I think these arguments are pretty convincing, and its surprising that the orthodoxy here is so entrenched.

"Economics textbooks" is the obvious joke answer. A more serious answer is that some right-wing thought emphasizes a certain kind of freedom (e.g. Nozick) so that there may be *very* many different equally utopian outcomes, and so no single vision to write about.

This sounds right to me too. The definition is strictly false, but for the uninitiated it's better at conveying the spirit of the enterprise than many more careful definitions might be. (cf. "philosophers ask questions that come naturally to children using methods that come naturally to lawyers")

(Obvious rival hypothesis: Someone - though so far as I can see, not Epicurus, or Hume - introduced the problem with reference to omniscience, and everyone since has blindly copied that person in deference to tradition.)