morality is subjective and people don't have free will

[Aroura]

It's as objective as science. All the arguments made against a science of morality can be made against a science of health.

And no, it's ontological objectivity that is absurd. The idea that morals exist "out there"... apart from our subjectivity. But epistemic objective morality makes sense. The idea that there are right and wrong answers in principle to increasing and decreasing what we all value and care about: i.e. well being and suffering. That's analogous to the idea that there are right and wrong answers in principle to increasing and decreasing what's good and bad for our health.

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Also, I can test for the existence of something (harm), but assigning en emotional value to it is what makes it subjective.

Ontologically subjective, but still epistemically objective.

 I can objectively say that oxygen molecules exist.  Adding that Oxygen is good because mammals breath it, is subjective.

It's an epistemically objective fact that oxygen is good for the ontological subjectivity of all mammals.

I don't know.  I dislike using the word "good" here, I would say necessary.  Oxygen is necessary for the existence of the animal.  But saying it is good, means that the existence of the animal is "good" for the animal, and I know you would debate that point, as you have claimed you are an anti-natalist.

Good implies that the existence of the animals has an objective quality of goodness, but good is an entirely subjective term in the first place.

This appears to much like the supposed conundrum that a doctor cannot determine your pain. But much like a physician saying that your back hurts, the hurt objectively exists.  The doctor can detect the damage that causes your pain.  The quality of the pain is subjective, though, and must be left to the person experiencing it to relay, the doctor cannot objectively tell you what that is.  This is the subjective part, just like with morality/harm/suffering.

The damage/harm is quantitative, measurable.  The suffering/morality we assign it is qualitative; different people or groups of people might assign different suffering/moral values to the same measured damage/harm.  

As far as I can tell, epistemology is irrelevant here.

p.s. I agree many people conflate fatalism with determinism.  We are more than rocks, and even rocks change over time.  We have desires, and can act in accordance with those desires.  But as you've pointed out, having desires and being able to fullfill them do not = free-will.  Compatibilism is silly.