The more I think about value monism, I get confused about why some people really want to cling to it, even though our own experience seems to tell us every day that we are in fact not value monists. We care about many different values and also care about what values other people hold. When we ask people who are dying most of them will talk of friendship, love, and regrets. Does all of this just count instrumentally toward one "super value" such as welfare or are there some values we hold dear as ends in themselves?
I came up with a short experiment that can maybe act as an intuition pump in this regard. I would be interested in your thoughts!
Thought experiment: What do we care about at the end of time?
We are close to the end of time. Humanity gained sophisticated technologies we can only imagine. Still, only two very old humans remain alive: Alice and Bob. However, there also remain machines that can predict the effects of medicines and states of consciousness and lived experience.
It seems like the last day for both Alice and Bob has come. Alice is terminally ill and in severe pain, Bob is simply old but also feels he is about to die a peaceful death soon. They have used up almost all of the medicine which was still around, only one dose of morphine remains.
The medical machines tell them that if Alice takes the morphine her pain would be soothed but the effect would not be as strong as normally due to her specific physiology which dampens the effect of morphine. Bob on the other hand would have a really great time if he took the morphine. His specific physiology is super receptive to morphine. He would experience unimaginable heights and states of bliss. The medical machines are entirely sure that net happiness would be several times higher if Bob would take the morphine. If Alice would take it, they would simply have one last conversation and both die peacefully.
How should Alice and Bob decide? What values are important in their decision?
This position seems confusing to me. So, either (1) ethics is something "out there", which we can try to learn about and uncover. Then, we would tend to treat all our theories and models as approximations to some degree because similar issues as in science apply. Or (2) we take ethics as something which we define in some way to suit some of our own goals. Then, it's pretty arbitrary what models we come up with, whether they make sense depends mainly on the goals we have in mind.
This kind of mirrors the question whether a moral theory is to be taken as a standard for judging ethics (1) or a definition of ethics (2). Even if you opt for (2) the moral theory is still an instrument that should be treated as useful means to an end-in-view. You want the definition to be convincing by demonstrating that it can actually get you somewhere that is desirable. Thus, it would be appropriate to acknowledge what this definition can and cannot do so that people can make appropriate use of it. Whatever road you chose you still come to the point where you need to debate which model "works" best. That's the beauty of philosophical and ethical discourse.
And turning back to the question of value monism, I think Spencer Greenberg has some interesting discussion for people who are moral anti-realists (people who fall in camp 2 above) and utilitarians. Maybe that's worth checking out.