Surely, a piece of literature can be objectively suggestive of both an attempt to get the reader to approve of something *and* of equally objectively suggestive of an attempt to get the reader to mock that thing (suppose that these reactions are filled in so that it's impossible to do both at the same time).
I mean compare: there are definite objective facts about the meaning of english sentence "Meet me at the bank" - facts which determine that it is ambiguous between two specific things: an invitation to meet the speaker at a financial institution vs. an invitation to meet them at the bank.
So: saying that there can be multiple, incompatible readings that are equally strong (e.g. readings that differ as to whether a given question is rhetorical) does not establish that there are not objective facts about how strong each reading is!
ok, now i will try to stop being so cranky :)