If I'm understanding what you're saying here correctly (which is far from certain), I agree with you that what moral systems I endorse depend on what I assign value to. If that's all you meant by morality not being fundamentally rational, then I don't think we disagree on anything here.
Cool! I assume what I assign value to is largely determined by evolution. That my ancestors who had very different inborn value systems didn't make it (and so are not really my ancestors) and the values I have are the ones that produced a coherent and effective organized cadre of humans who could then outcompete the other humans for control over the resources, as a group.
To me it seems irrational to assign much weight to these inborn values. I can't say I know what my choice is, what my alternative is. But an example of the kind of irrationality that...
Suppose I have choice between the following:
A) One simulation of me is run for me 100 years, before being deleted.
B) Two identical simulations of me are run for 100 years, before being deleted.
Is the second choice preferable to the first? Should I be willing to pay more to have multiple copies of me simulated, even if those copies will have the exact same experiences?
Forgive me if this question has been answered before. I have Googled to no avail.