Are there any "canonical" (or at least, quite good) papers that attempt to justify the supposition made in the model theory for classical first-order logic that the domain in non-empty?
I know that free logic was developed (at least in part) to avoid this assumption, since "something exists" doesn't seem (to many) to be a logical truth.
Intuitively, I could see the assumption being justified in something like the following manner: you cannot have a logic that quantifies over individuals without there being at least one individual. In this sense, it is just a necessary presupposition, but perhaps not to be regarded as a "logical truth" in the same sense as the law of excluded middle might be.
Is there any literature discussing this issue in the philosophy of logic? In particular, any literature which attempts to defend this assumption?