I don't know as much about labour theory, as you seem to think I do. I'm not trying to argue for any ideology and I find the reduction to a duality between supply-demand and labor-entitle overly simplistic. Those are ideological landmarks, for sure, but both are volatile in nature and both happen, whether it's allowed or not (even though the decision to allow is a big one).
Since you asked me about a constructivist model of value, let me try at a sketch (and put qualify with "in my mind" as necessary):
First and foremost, value is information, because it's a relation over facts, so relates facts to one another, puts them in perspective. What I think many people would call "true" or "real" values are those that can easily be considered facts in and of themselves, because all their relatives are known facts.
Those values, when considered closely, are few and far between and many intellectual currents, including science, have been devoted to finding more of them.
Social constructivism (a category, that includes capitalism as well as marxism, basically every model talking about people doing things with their lives), has the inherent problem that many of its facts are unknown. That's because people keep them secret, because they are part of their private lives, that they don't want other people to know about. Also, people change over time and so do their private facts.
Hence, in social sciences, it's _even_ harder to find meaningful true values and successful models have to account for large degrees of individual freedom.
Coming back to your argument, I categorically agree, that supply-demand creates untapped demand. I don't categorically agree, that that's a good thing. More concretely: Sure, free expression has promoted many good things, still, everybody has their own line about what they want to be allowed to be promoted and/or even sold.
In practice, I think for a functional state, it's much more common to defend the free market against yet another asshole that just found out that destructive behavior can give you a temporary advantage, but didn't quite figure out the calculation of long-term costs and / or doesn't care.