The Space Aliens and the Ontological Ground for Moral Facts

I've said before that you know that you do philosophy when you dream philosophy. Kenny recently had a dream that would actually make an excellent science fiction story in the right hands:

In my dream, some space aliens discovered that platonism was false. They were very disturbed by this because, they thought, without platonic objects, there was nothing to serve as the ontological ground for moral facts. So the aliens convened a galactic council, and held a sort of lottery. Earth lost the lottery, so the aliens were rounding up all the humans and putting them into a simulation. In the simulation, the humans would have every possible experience. The choices made by the humans in the simulation would then provide the ontological ground for moral facts. Then I woke up. (Either that, or I'm presently in a simulation designed to create moral truths; I suppose I'm not really sure which.)