Thank you so much for your post!
So a being that is perfectly good can create evil and still be perfectly good?
Of course! By manifesting the contrasts which are the creation, God created good where there was only unity (infinite nothing) – but again, good only exists by contrast, so evil was created as well. This is how He revealed His will, His nature, His goodness. He also created beings with free will and communicated His will through His Word which encompasses His moral law. The knowledge of good and evil was not intended for all the beings with free will. But having obtained that knowledge, man now has the duty of the moral law.
No, I'm not saying that the substance of it is objective, but that the fact of its existence is objectively true. I mean, either it is or it isn't - forget about what it is, surely you believe that it exists in an objective sense.
Moral law exists absolutely. We can objectively say that God's absolute moral law exists. But the law is subjective in enforcement. People who have not received the moral law of God will be judged by their conscience (Romans 2:14-15) – people who have received the law but not Christ will be judged by the law (Romans 2) and believers such as I, although free from the law (Romans 8) are bound to a much higher, spiritual standard (Matthew 5-7) And all of this is on top of societal laws to which must also comply (and hope are compatible with the absolute moral laws of God.)