You've given a radical example. It's less obvious when you compare egoistic and altruistic attitudes, as in Gorgias. The evolution itself, as scientific theory, is blurring the border between good and "efficient" behavior. There must be some scientifically proved scoring rule for comparing "bad" and "good" societies, if science can tell us what is wrong. Otherwise it would not be a science ;) I don't claim that you're wrong, but it is very hard to preserve moral values in an atheistic ideology. Of course, you can identify "good" with "pleasant" or "increasing probability of reproduction", but IMHO it can't give you a proper view of morality. BTW your reasoning (why is-ought is false problem) didn't give ma a positive solution about source of the moral values in human actions.
I highly recommend 'Practical Ethics' by 'Peter Singer'. You will start seeing how you can apply critical thinking to various moral questions in life without clinging to any religious book. If there are facts to learn about human happiness then 'science' only(this includes economics, history, philosophy etc, basically all forms of rational discourse which are open to criticism and change) should suffice.
There is some good advice in Bible but there is lot of crap too and if you choose to cherry pick, its fine. Just keep in mind that your innate morals themselves are making you pick and choose. It was not written for a person in 21st century whose world is unfathomable for the Bible's author.
> I don't claim that you're wrong, but it is very hard to preserve moral values in an atheistic ideology
What do you mean by 'preserve'? Why can't moral values evolve overtime? At this moment, people eat mammalian meat happily without concerning about torture that those animals go through. I have no doubt that 100 years from now, people will look at this tradition similar to how we find slavery now. Slavery was so prevalent(and useful) that there seemed to be nothing 'wrong' with it. No surprise, that Bible didn't mention anything against it. But society evolved and soon it became something unthinkable. Some act which was not wrong, suddenly became very wrong. Similarly many moral values were not 'preserved'. I hope you see my point(literally and metaphorically).
