It seems to me that when conversations get to that level, every participant has to either:
- claim to be a relativist (at which point I bow out
)
or
- state the axioms they use as foundations for their philosophical stance.
To me, it mostly boils down to a comparison of (by definition), unprovable axioms.
For example, I borrow and extend from Sam Harris: "It's 'good' to act in ways that maximize the well being of conscious creatures for as many generations as possible." (WBMG)
I acknowledge that I cannot prove my axiom. I cannot prove that such actions are "good".