Consider this "easy ontology" argument:
- There are no unicorns.
- So, there are zero unicorns.
- So, there is a zero.
- Every leprechaun is a fairy.
- So, the set of leprechauns is a subset of the set of fairies.
- So, there is a set of leprechauns.
- If there is a set of leprechauns, it's empty. (There aren't any leprechauns!)
- So, there is an empty set.
- Every non-self-membered set (set a that isn't one of its own members) is a set.
- So, the set of non-self-membered sets is a subset of the set of all sets.
- So, there is a set of non-self-membered sets (the Russell set).
What to do? One move is to make the easy ontology arguments defeasible. This isn't in the spirit of the game. The other is to add to the premises of the easy ontology argument a coherence premise: that there is a coherent theory of zero, of the empty set and of the Russell and universal sets. The coherence premise will be false in the Russell case but will be true in the other cases. But the point is one that should make us take easy ontology less easily. (I wouldn't be surprised if this was in the easy ontology literature, with which I have little familiarity.)