How do these values get proposed and accepted or ruled out? And, who gets to make those decisions?
How do you get people to accept your ideas and put them into practice?
Human values need to be discovered in the very same way any scientific invention takes place. It has to be part of the conscious effort that people make towards inventing the society next.
Human values cannot be proposed as precepts handed down by any individual or groups, how ever noble or powerful such persons might be. Truths live by themselves and do not need the support or approval of any other. It is for the humans to find these individually and collectively.
Knowledge of truths benefits humans. It is by knowing the truth that a certain mosquito bite causes malaria, people could invent an antidote for such infection. Humans are better off by knowing more and more of truths.
The very same logic applies to human values as well. It is by discovering and learning the truths about human values, quality of life can improve.
Discovery truths can be as simple as a sudden spark inside the brain or a long drawn process involving years and years of research. It is simultaneously a function of the pre-existing knowledge and forward thinking. Truth might elude our grasp still, in spite of the rigorous methods we adopt, if we are not open towards it and are not absolutely honest and sincere in its pursuit. Truth reveals itself only to those who seek it without having any preconceived notions or prejudices that filter out that the facts reaching the brain.
There are of course a few inherent limitations in the process.
1) Even after discovering truths, it will need to be communicated appropriately for benefiting from it maximally. While one might benefit personally from any discovery of truth, maximum benefits would accrue only when it is utilised by the society as a whole.
2) Social acceptance of truths takes time depending upon the relevant urgencies as well as the vested interests working against these. Since truths are discovered by individuals, who will be in a minority initially, established social groups might torpedo its social acceptance.
3) Societies and human mindsets have not matured adequately to recognise truth independently by disassociating it from the persons who discover it. Most mindsets are attuned to judging facts based on the profile of its advocates. People will need to develop an attitude for evaluating truths independently of its proponents.
4) Knowledge of truths can never be absolute. Planet earth was once considered to be the centre of universe. The more open and willing people are towards understanding newer postulates and evaluating these objectively, greater will be the chances for the world to become a better place for all.
The above process applies to the discovery of truths about human values as well.