I can work in heavy boats or light boats. It depends what the client wants. Both types have their distinct advantages. If you are going offshore and want lots of tankage you are not going to get it in a light boat. PERIOD.
For me displacement will be a fucntion of the intended use of the boat coupled with the owner's preferences and sailing style.
As I read this, (and some of MikeJohns comments) there is a piece of this quote that I would like to comment on and hear both your's and Mike's thoughts. I know that I have stated my viewpoint on this on any number of occasions around here and its a position that Paulo perhaps would agree with as well.
I think that the terms " heavy boats" or "light boats" are somewhat misapplied in common usage. In my mind, these terms get applied in a manner that is shorthand for "heavy boats for their length" or "light boats for their length". My sense is that that partricular 'shorthand' sends the wrong message.
When I think about how 'big' a boat needs to be for any given owner, it starts with its stated purpose in terms of where and how the owner's plan to sail the boat, how many people are involved. That somewhat dictates the carrying capacity and the need for more or less robustness.
Once you get to a needed carrying capacity, and bearing in mind the need for more or less robustness, from there I would think its pretty easy to back into an approximate target displacement for that vessel fully loaded and from there its capacity empty.
At that point it becomes a question of picking the "just right" length. I know that there are folks who prefer a short boat for its weight. But disregarding those folk's personal preference for a moment, I suggest that the science would say that, within reason, a longer boat of the same displacement and robustness is likely to offer better accommodations, better motion comfort, more seaworthiness, and better performance than a shorter boat of the same displacement. The longer for its weight boat should also be easier to sail to sail since it would be easier to design the boat with more stability, and a more efficient keel, rudder, and sail plan.
So, if I were going distance cruising I would inherently choose the longer boat for its displacement, specifically to improve seakindliness, with the improvement in performance being a secondary consideration. That would of course fly in the face of the US court of public opinion, which says, using the usual shorthand, "a heavy boat (for its length) is more comfortable" when in fact the reality is a longer boat for its equal weight is more comfortable.
In reality, when you look at the trends in what we normally might think of as modern distance cruisers, they are tending towards being longer boats for their weight, and seem to deliver a more comfortable motion than shorter equal weight boats. That trend has been going on nearly as long as the 50 plus years that I have been sailing.
But the other oddities of perception which does not seem to make sense is the way that D/L's are bandied about. Obviously, there is a good reason for L/D being based on waterline length. But over the period that I have been sailing, waterline length has gotten progressively longer relative to length on deck. I keep hearing people talk about the motion comfort of the good old boats with L/D's in the high 200's but in reality, modern boats are not all that much lighter for their lengths on deck. They just have longer water lines which make these boats appear to be much lighter when comparing L/D's. The real gotcha in that, is that if we compare two equal length on deck with equal displacements, all other things being approximately equal the boat with the longer waterline is likely to have the more comfortable motion. That of course also flies in the face of the beliefs rendered by the court of public opinion.