My recollection is that this was someone currently alive, writing in the 1970s or later.
And the sense of the quote was not that there could be nothing more dishonest, but that there were few things more insidious in their dishonesty than a question wrongly posed.
Take, for example, the sort of question that asks, “Are the people who believe X crazy or stupid?” There is noting in the question that suggests that the person who asks it is in any way interested in finding common ground here, or the question would have focused on some aspect of it. The whole purpose of the question is to draw out the person who feels honor-bound to defend in X, even if it makes them look ridiculous.
Not all questions of this sort are so leading and transparent. For example, in another forum someone asked, “What have the conservatives done to benefit the American people?” On the surface of it, this sounds like a fairly straight forward question; but, in reality, it was just thinly disguised troll bait, because what one side saw as a “benefit” the other side saw as an anathema.
What’s really dishonest is that each side thinks they are engaging in legitimate argument, while it is the other side that is acting crazy or dishonest when the rhetoric becomes more polarized and inflamed. It gives people the impression that their opponents cannot be reasoned with. So the only purpose of engaging in debate is to embarrass or humiliate one’s opponent. This is the sort of thing that causes civilizations to fall into decline.