Suppose that there is a set of all good things, and that it is well-founded. Then it would not be an element of itself, i.e. would not be a good thing. Maybe it would be hypergood, but maybe it would be neutral; for it to be evil seems unlikely/impossible.
At any rate, one might expect that the universal set of goodness should be good, too, so one might be led to conclude that such a set (if it exists or is even at all really conceivable) must be at least a Quine atom of some sort, or akin to those anyway. However, then the cardinality associated with goodness is not well-founded. If not well-founded, is it incommensurable with sets of numbers that are well-founded?{!} If incommensurable with the n, perhaps the "moral numbers" (or quantities, anyway) would admit of a different sense of their arithmetic, too; this might be what G. E. Moore subconsciously (or consciously) considered to explain the possibility of "organic unities" of intrinsic ethical values.
{!}Suppose there were a set of all sets that are commensurable with other sets. If indeed well-founded, such a set would not be commensurable with other sets. This, then, for a reason that is sort of an obverse of the above, yet still a testament to the existence of incommensurability in general (not just the obscurely abstract possibility of it, either, though note that many are moved to incommensurability/incomparability claims in ethics on intuitive grounds).