Sean, first we have to take the ubiquitous modern length equation out of it and think in normal mortal golfer's terms. The bold shot is at the pin, challenging Hell and going at the pin either in the air or run up through the channel between Ginger Been and the knob to the right of green. If an intimidating bunker is behind the pin, the golfer is discouraged from accepting the primary challenge over Hell and threading the needle or flying and stopping it, because of a second threat of the rear bunker. Now, perhaps that golfer is only thinking safe lay-up to the left, or even a lofted shot over Hell and short of the green. No more heroics, if one has to take on three challenges, Hell, Ginger, and rear bunker.
I believe if we read on, Hunter talks about the economy of using the bunkers sparingly, and I think he is making the point that this rear bunker is one too many, discouraging bold play by discouraging the heroic because it would turn into the idea of taking on one too many...