Is it true that there is no absolute morality?

[Nonpareil]

The experience of ideas is certainly subjective and not objective.  However, that's from inside the system.  For anyone outside you, everything you think and do is 100% objective.  They can see your facial movements, watch your brain blood flow in an fMRI, stick electrodes on your head and so on.

So are you arguing that a moral system is only an idea to be experienced subjectively, and not more than that?

The existence of thoughts is objective fact.

The value system defined by those thoughts also has objective existence, inasmuch as any concept does. The opinions offered by this value system remain subjective, because whether or not they are "true" depends on whether or not you share the same basis for making value judgments.

Moral systems have objective existence; it is objectively true that someone has thought of them. The opinions contained within that moral system are only subjectively true; whether or not you agree with them is contingent on you sharing the same basis for value judgment. In the same way, it is objectively true that I have opinions on which movies I consider "good", but whether or not you agree with those opinions is subjective, because it depends on whether or not you have the same criteria for defining what a "good" movie is.

This is not complicated.