Just to make things abundantly clear, I would first like to make 2 points.
First, truly appreciate the dialogue between you 3. Thank you, all of you, for your thoughtful, insightful, discussion without rancour, self promotion, belligerence or pride. May we have many more of those, as they are a great example to the rest of us as to how a conversation may be carried on, even though there may be disagreement on some particulars.
Second point. I'm beginning to wonder if I missed out on something. (Not marriage, now going on 46 years, praise God ) but the military thing. When I was 17, in my country of NZ, we had a draft system whereby ipf your birthday date came up, compulsory military training was inevitable at the local base, which was situated near the top of a mountain range surrounded by snow, ice, and nothing much else. My date came up. I had 6 months to prepare mentally for something I dreaded. This was not for me, not in any way I could imagine could I consider myself military potential.
2 days before I was due to depart for a cold hell, the government scrapped the whole idea. Effective immediately. What did I miss? I will never know. Possibly a positive life changing experience, or, God knew where He did not want me, and altered the course of NZ history just for me.
Back to the topic at hand...
For some reason we get the wrong impression about morality, believing that right and wrong didn't exist until God laid down the rules. This isn't true at all. Cain inherently knew that murder was wrong. He didn't need a commandment from God informing him that it was wrong.
I agree. Morality, right and wrong, or at least the right, has been around for as long as God has lived. And Adam and Eve were created in the image of God, which I would suggest was not only in appearance, but in character as well. However, that "created in the image of God" motif that began with Adam, ended with him as well. For we read in
KJV Genesis 5:3
3 And Adam lived an hundred and thirty years,
and begat a son in his own likeness, after his image; and called his name Seth.
I would think that Cain and Abel were also born in the image and likeness of Adam. I also think that we tend very much to grossly underestimate how rapidly and how deeply Adams sin affected not just mankind as a whole, but even himself and his immediate offspring. So while I agree with you that there would have been a modicum of moral consciousness in the hearts of Adams descendants, as there is to this day unless completely hardened by sin, Cain's personal moral compass was already adversely damaged as evidenced by his reluctance to obey God's requirements for sacrifice, and trust in his own ideas on how worship ought to be undertaken, based on pride, presumption, self confidence, arrogance, self will... In short, all the same rebellious self promoting mindset of Lucifer's rebellion in heaven. If Satan was a murderer from the beginning, then that same callous disregard from life was in Cain also. It seems the depravity of man and the enslaving power of sin very quickly overcame any desire to resist, even after a personal warning from God Himself.