Why not? Am I the one proclaiming all value is objective? I think not. You are the one arguing objective value doesn't exist. You seem to be the nutjob needing to justify your extreme characterization of the world, whether we are referring to human behavior or otherwise.. but then you are saying the world does not matter, except to the extent that humans value it?
It is not an extreme characterization. In fact, it is the very fundamental principle of sound economics. "Objective" adheres to impartiality, and is a reference for something that has properties that can be verified, regardless of opinions. The meter is an objective unit of measurement, because it refers to external, natural phenomena that occur regardless of perceptions.
But, value is not referring to anything external. It is defined only by the person's judgement. A bottle of water remains the same bottle, whether it is sitting on a desk or found on a deserted island. Yet, a person dying of thirst would clearly value it differently, depending on the circumstances.
For value to be objective, there would need to be a unit of measurement that is independable of human preference, but that contradicts the definition of value, as something is valuable only for someone and is not intrinsically for itself.
Also,
The subjectiveness of valuation rests in the nature of satisfaction--satisfaction is subjective and not open to numerical measurement. The extent to which a thing gives satisfaction is always personal. People derive satisfaction from different goods and services; that is, all people are not alike in terms of the types of things that please them. Experience also demonstrates that a person’s preferences vary from time to time. His ranking of alternative choices may undergo a reshuffling at any given moment. His scale of values may also be altered by deletions or additions.