The notion of "objectively better" is an analytic contradiction in the same sense as is "concrete abstraction". Furthermore, preferences are relative, not absolute. "Better" and "worse" (and similar words) describe preferences, and preferences are relations between physically real state of affairs to minds, i.e. subjective entities.
Furthermore, preferences are relations not to the low-level physical characteristics of minds (i.e. they are not relations to neurons), they are relations to abstract, high-level arrangements of whatever physical substrate the mind on which the mind is instantiated.
Some of our preferences, of course, relate to gross physical characteristics of our bodies and brains. When we are hungry, we ordinarily prefer to eat food; when some of our sensory neurons are stimulated, we feel pain and ordinarily prefer its immediate cessation. But this is just to say that some of our abstract subjective characteristics have a direct relationship to some physical properties of our bodies and brains. But there are those who prefer to experience the physical sensations usually labeled as "pain", and there are those who feel little subjective distress at the sensations usually labeled as hunger. A purely physical comparison between such people and "ordinary" would reveal no difference in the gross physical characteristics of their bodies, but differences only in the abstract arrangement and connectivity of the neurons of their brains.
As Stephen J. Gould spent most of his career showing, our physical characteristics are to a considerable degree accidents of historical evolution. While physical law and the constraints of evolution preclude some forms, they permit vastly many more forms. Only a minuscule fraction of possible forms have ever found expression in the four billion years of terrestrial life. Our present forms, both human and non-human, owe as much or more to the pure luck of which organisms happened to survive global catastrophes than to inviolable constraints of physical law.
Thus, even many preferences grounded on deep physical characteristics of human beings — especially those more sophisticated than hunger and avoidance of pain — can be considered in a substantive sense to be arbitrary accidents of evolution.
Some of our preferences are established not by our biology, but by our culture and society. We in the West have, for instance, come to agreements about preserving freedom of speech (and even that agreement is not as solid as we would like). Socially constructed agreements are self-perpetuating in the same sense that our genetic heritage is self-perpetuating: I prefer freedom of speech (and I really do prefer freedom of speech) because I was socialized in a society and culture which most of the people preferred freedom of speech. Had I been socialized elsewhere, it's probable that I would not prefer freedom of speech. (In just the same sense, I have two legs because my parents had two legs, and I share their genetic heritage.)
Attempts to reduce these sorts of socially constructed agreements to even to biology, much less some sort of abstract norm fail on the evidence. That some socially constructed agreement such as freedom of speech cannot be necessitated either by physical law or the general properties of human brains, because we can observe that people lived for hundreds of thousands of years — and billions of people currently live — without such agreements.
(Of course, there are some agreements that cannot be socially constructed, or at least not for long. A large-scale society and culture that prefers not to physically reproduce will not be around for very long; any group of people (myself included) who do prefer not to have babies will always exist within a larger culture that does prefer to have babies. But as we see in biological evolution, the notion that some forms are prohibited does not entail that one single form is necessitated.)
And, of course, some of each person's preferences are the result of nothing more than the personal genetic and environmental accidents which have led to her present mental state. Furthermore, some of these preferences are persistent, but others can be capricious, changing from time to time, some never to return.
I don't want to diminish the importance or value of individual preferences and socially constructed agreements by categorizing them as accidental, subjective, and self-perpetuating.
The subjective is, of course, real: minds are real abstract properties of real physical brains. And just that any particular form is the result of accidents is still to acknowledge that the accidents really happened, and here we are, stuck in our present forms.
[Ugh. Too many many mistakes. I'll clean it up later.]