There is a very fine argument in Ockham's Summa Logicae book II, chapter 4. He is objecting to the claim that the verb 'to be' is ambiguous in certain arguments. But this is completely irrational, he says " for it amounts to destroying every argument form. For whenever it pleases me, I will say that 'to be' is equivocal in the premisses, and I will ascribe at will a fallacy of equivocation to every syllogism".
Absolutely right. The verb 'is' is implicit in every proposition. If this verb is ambiguous, we can disprove any argument whatever at will, by appealing to this ambiguity or equivocation. But that is irrational, and amounts to destroying all logic. For logic is about the form of arguments, and not about what we can 'ascribe at will'. If we can challenge the validity of any argument 'at will', you destroy all logic.
This claim that Ockham objects to is precisely the claim that Jody Azzouni appears to be making when he argues against the 'triviality thesis', which is the thesis that the existential quantifier just means 'there is', and 'there is' just carries ontological commitment. Azzouni argues that the triviality thesis is wrong since there are assertions of the form 'there are Fs' that do not always carry ontological commitment.
If Azzouni is correct, it really does amount to destroying all logic. I have already argued this in my objection to William Craig's claim that there is no contradiction in 'some x's are numbers and no numbers are created' and 'all x's are created by God', by reason of equivocation on the existential quantifier. If an argument as basic as this is invalid, all argument is invalid.
Here are two more arguments for this.
1. Meinongians say there are fictional entities. Nominalists say 'there aren't'. Regardless of what is the correct position, this disagreement could not take place at all unless both sides were agreed on the meaning of 'there are' and 'there aren't'. When the nominalist says that there aren't any fictional entities, he is denying exactly what the Meinongian asserts when she says that there are such things. The expression 'there are' is completely unambiguous in this argument, and has to be, in order that there can be an argument at all.
2. Azzouni might argue that (for example) 'there are hobbits in Tolkien' is true, but 'there are hobbits in Jane Austen' is false. But this is not an argument that 'there is' is equivocal. On the contrary, it means exactly the same in both cases. What is asserted is different, for in one case we say there are hobbits in Tolkien, in the other, that there are hobbits in Jane Austen. It is the qualifying 'in Austen' or 'in Tolkien' that changes the assertion. But in both cases 'there are' means the same. If it doesn't mean the same it amounts, as Ockham says, to the destruction of all logic.