Many great thoughts here, thank you for your comment.
I've heard similar critiques of the Golden Rule (and the Silver Rule) and I agree with them. Ultimately, we should treat others as they want to be treated in order to increase human wellbeing.
As to not disregarding your own desires, I've really enjoyed learning about objectivism and how, rationally, virtue is a wonderful ideal which maximizes our own wellbeing as we also consider the long-term benefit of others.
As far as I understand of "Natural Law" is that it emerges from what we observe about nature. It's not absolute, but again, a construct which serves us well and fits our observed reality. As you said, we could all be living in a simulation anyway, so any big "T" Truth we might claim could just as easily be an illusion, right?