To put it another way, how much is there that all linguists would be willing defend as correct knowledge about linguistics?
I have just finished taking an introductory course in linguistics. One thing that struck me was how at every topic there was always a disclaimer along the lines of "this is just one analysis" or even "orthodoxy has it that ... but it's not clear if anyone believes that". For example, the professor disagreed with the textbook's putting adverbs in the specifier position of verb phrases. This being a question at all depends on the validity of the X-bar theory, which I'm told is a theory of Chomsky's. And Chomsky, I'm told, revises his theories every decade or two, and you sometimes overhear the TAs discussing which version they were taught as undergraduates. And then I read that Chomsky's entire approach is questioned by large swaths of the linguistics community. Therefore it would seem that there isn't any consensus at all, which really makes the entire business rather suspicious.
To what extent am I exaggerating the state of affairs?