In your case, a simple "why?" would seem to be a fitting question. The VI could be seen both as good rule utilitarianism and a way to ensure distributive fairness. The question of "What sort of world do you wish to live in?" answered by a party unaware of any relevant distinctions between herself and anyone else seems as though it may be potentially instructive.
(BTW, I think my conversation starter was relatively innocuous and didn't merit belittlement.)
-- Luke