As a practical matter, if I believe in a "setpoint" for my weight, the SLD theory tells me I can temporarily "trick" my body into lowering my setpoint by taking shots of oil or sugar water or pinching my nose when I'm eating. But once I stop doing SLD, I'm doomed to return to my "setpoint" weight which is somehow (mysteriously) predetermined by genetics, or how I grew up, or God or fate or whatever. It is a somewhat pessimistic and fatalistic view, in that my body is a black box that I can't understand, and I can't really control the outcome over the long term without being stuck on this weird diet.
Except that Seth explains in his book that between meals, or when we skip meals, our setpoint is driven down, then raised again by the flavors/calories of the things we eat...the net effect of this process determines the setpoint (a mean of the ups and downs over time). This could be analogous to circulating insulin averaged over time, controlling appetite, etc., but the net effect is the same - a setpoint that can be altered by understanding the body's responses to food.
I can name for you the setpoints I have encountered in my adult life, ranging over many years, all while not dieting, with a huge range in activity levels (running 10Ks-sedentary) but clearly encountering setpoint altering events (or insulin/hormone system changing events/eating styles). As in 142 lbs for 4 years, 160 for 3 years, 180 for 6 years. I was not watching my weight at all, but found that it didn't change...until it changed substantially and then stayed at the next setpoint.
In this way, our total dietary patterns/hormone release trends add up to a setpoint for us at a point in time. The intervention method in SLD (of flavorfree calories) pushes down the setpoint in effect for a person right now. It can also be achieved in a more comprehensive throughout the diet approach (see The Rice Diet, by the Rosatis), where you change your eating patterns until you are eating foods that add up to lowering your setpoint. Whole foods, low glycemic load foods, bland foods are all foods which in Seth's experience drove down his desire to eat...I have the same experience.
You aren't doomed to return to your previous setpoint if you stop with oil/SW, noseclipping...you simply have to apply the same principles to all of your food/a great majority of your food. Less intense flavors, slowly digested foods, homecooked foods which are never exactly the same as the last time all are ways to maintain the new lower weight setpoint after loss.
The reason most of us try to stick with it is that our daily lives prevent us from being cautious enough to avoid raising the setpoint again. I guarantee that if I ate the early diet of Pima or Kosraen indigenous (or early Irish or Sicilian), all low flavor/calorie associated foods, my setpoint would remain low enough to satisfy me.
We are, in T. Colin Campbell's words, suffering from widespread "diseases of affluence," all resulting from a food habit which causes a plethora of problems, the most visible of which is obesity.