Let’s understand what moral subjectivism is by defining each word separately:
Subjectivity: “Existing in the mind; belonging to the thinking subject rather than to the object of thought”
Morality: “The differentiation of intentions, decisions, and actions between those that are distinguished as [good] and those that are [bad].”
Value is what determines what is morally “good” or “bad”
Value: “Deals with right conduct and good life, in the sense that a highly, or at least relatively highly, valuable action may be regarded as ethically ‘good’ (adjective sense), and an action of low in value, or somewhat relatively low in value, may be regarded as ‘bad’”
So when someone says morality is subjective, they’re saying what constitutes as “good” or “bad” is the subjective value assigned to it by the individual. “Okay but that’s still doesn’t explain how they’re wrong” you say. But let’s add a fourth vocabulary term, value-judgement. Now there a variety of definitions for this term but I’ll define it as followed:
Value-judgement: “the judgment of the rightness or wrongness of something or someone”
So is there a difference between having subjective values and subjective value-judgements? Does one imply the other? Yes there is and no it does not! Subjective value is an ontological doctrine while value judgements are a metaethical doctrine. I argue that the former is subjective and the latter is objective, but not in the conventional sense of objectivity, I’ll explain later on.
First, how can this be? Subjective value means that values exist because of human consciousness. If we didn’t exist, then nothing would have value. Objective value judgement means that we can have knowledge of value, whether the value is “good” or “bad”, or “valuable” or “valueless”.
For example, Sartre in Being & Nothingness describes a man walking into a cafe to find his friend Pierre, who is not there. Pierre’s absence is constituted by consciousness, but is also dependent on the actual fact in the world that Pierre is not there. A thing’s (e.g., my phone) value is created by me but also depends on objective facts in the world (that my phone exists).
But goodness is not out there like an object such as my phone but that doesn’t mean that we invented it or that something’s being good is based only on our feelings of it. We can recognize its existence by looking at evolution.
Roll back on natural selection of individuals and just imagine a community of individuals where anything is permissible, even murder. James Rachel’s says that:
“In such a ‘society,’ no one could feel secure. Everyone would have to be constantly on guard. People who wanted to survive would have to avoid other people as much as possible. This would inevitably result in individuals trying to become as self-sufficient as possible—after all, associating with others would be dangerous. Society on any large scale would collapse. Of course, people might band together in smaller groups with others that they could trust not to harm them. But notice what this means: they would be forming smaller societies that did acknowledge a rule against murder. The prohibition of murder, then, is a necessary feature of all societies. There is a general theoretical point here, namely, that there are some moral rules that all societies will have in common, because those rules are necessary for society to exist.”
We can see here that although mortality, both for the individual and for society, might not be literally objective, this does not mean that it must be purely subjective; it may be functionally objective. Certain basic moral strictures are necessary for a society to go on existing. For any individual and community of individuals to exist now and to go on existing, they must behave in a way that is conducive to the existence of a society.