What you're describing is not evolution by natural selection.I'm not sure why this type of point animates you so. It IS still possible that the moral code is instinctual in humans and stopping a murder is equally valuable for the person.
You insist on saying there was "no mutual benefit" but you are 100% wrong. In fact it is kind of where your whole argument fails. There IS a mutual benefit. Each member of society is benefited by the security and safety of that society. If someone is going around and murdering other members of that society it is IN THE IMMEDIATE BENEFIT to EVERYONE in that society to stop the murder.
So your point is simply wrong from the outset. What follows from that is equally flawed for that reason.
Evil would be that which threatens our survival and the survival and propagation of our genes. Why is that a bad definition?
That's fine.
Wrong. Evil would be defined as that which threatens survival. As such biology has a WHOLE LOT to say about it.
Why assume that? Because many people don't like what is being found now early on?
Probably not. It will, however, require people to accept what science says even when it doesn't say what we want it to.
Evolution by natural selection is not about saving the species.
It's about propagating one's own genetic information, even at the expense of weaker or more ill-suited members of one's own species. Evolution was never about ensuring every member of the species was protected and nurtured.
What you're doing is carving out special exemptions for humans from the accepted Darwinian tenets of evolution by natural selection.
That is a massive retreat from the way this thread started, where the atheists claimed morality was based on evolution and we really weren't basically any different from the other animals.