Taken literally from a modern US English viewpoint, the phrase "few would argue that" would mean that the statement the phrase appears before is widely held to be false. The specific wording would either being hedging or accounting for a lunatic fringe, e.g. "few would argue that the Earth is flat." In my perception this is the far more common use of the phrase.
I have, however, come across a number of uses where, contextually, its clear the author intended just the opposite. One example is from Michael A. Stackpole's Coupe, in which a character opens a speech about war with "Few would argue that warfare is mankind's oldest profession - and oldest obsession." From context, its clear he meant something like "Few will argue with me when I say," or "It's not controversial to say."
Is one usage more common than the other? Or is this one of those things like "nonplussed" that has two widely used but contradictory meanings?