Why is this is problem?

Well, "asked in an insistent manner" does seem to count as evidence that there's some ulterior reasoning behind the question. Ordinarily I expect a lot of people (though maybe not most people) would be happy to admit that they've e.g. fantasized about running over Justin Bieber or whoever their least favorite pop star is with a tank, but I for one would be a lot more inclined to dodge the question or lie outright if my conversational partner seemed a little too interested in the answer.