A “utility function” as applied to humans is an abstraction, a model. And just like any model, it is subject to the George Box maxim “All models are wrong, but some are useful”.
If you are saying that your model is “humans … [have] a utility function at any given point in time, but not one that’s consistent over time”, well, how useful is this model? You can’t estimate this utility function well and it can change at any time… so what does this model give you?
A “utility function” as applied to humans is an abstraction, a model. And just like any model, it is subject to the George Box maxim “All models are wrong, but some are useful”.
If you are saying that your model is “humans … [have] a utility function at any given point in time, but not one that’s consistent over time”, well, how useful is this model? You can’t estimate this utility function well and it can change at any time… so what does this model give you?