From the Wikipedia article:
Argumentative is an evidentiary objection raised in response to a question which prompts a witness to draw inferences from facts of the case.
For example, if a lawyer on direct examination were to ask his (My Note: or her) witness, "So he was driving negligently?," opposing counsel could raise an argumentative objection. This is because negligence is a legal term of art, and the witness cannot reasonably answer the question. Since the lawyer is "arguing" his (My Note: or her) case through the witness, the objection would be sustained, and then stricken from the record. (My Note: I guess what is meant is '...then the question would be stricken...')
So what is the adjective for questions that do not ask to draw inferences or, I guess additionally, to state opinions? I think not 'objective' otherwise we might say 'subjective' instead of 'argumentative'. Same for 'direct': 'indirect'
Update: I can't believe I didn't say this before, but I believe factual vs argumentative relates to, respectively, positive vs normative.