We here are largely aware of Robertson's comments not because they have particular merit as a thought experiment, but because they occupy the sweet spot of maximizing controversy. That is, it is easy to present as objectionable within Blue Tribe, and easy to present as defensible in Red Tribe, and so in the end it's a fairly textbook toxoplasma. This isn't to say that the general question isn't interesting; it's just more important than usual that interested parties treat the thought experiment like a finger pointing to an interesting argument.

Personally, I find it fairly interesting that Robertson (et. al.) is concerned with assigning moral legitimacy to his outrage at suffering these various horrible events. Going to the extreme case has the advantages that Scott articulated, but it also seems to blunt the perceived need for a complex ethic. The things are 'bad' in the sense that any sane person would be deeply unhappy if they occurred; what is the point of invoking a whole metaphysics to justify that near-universal impulse? Wouldn't it be more interesting to focus on the places where an objective moral system would produce different results?