Is it only liberals and atheists that agree with moral relativism and comparative ethics?

Yes, it would be hypocritical to condemn genocide in the Bible if one thought morality is nothing but opinion. If morality is simply opinion why should your opinion take precedence over the contemporary believer's opinion? Why should your opinion be followed and not the other way around?

But not all atheists are moral relativists. I for example happen to be an atheist who thinks morality is more or less objective, that it's not just opinion but that genocide is actually wrong. Visible atheist figures whom I know believe morality is not just opinion include the neuroscientist Sam Harris and the Harvard psychology professor Steven Pinker.

I think your premise that Atheists' morality based on societal betterment is actually far stronger and more morally superior to Christian morality. Just because it isn't based on an old book, doesn't mean it is weak. There is strength in that morality that you can't get from a book.

And why do you say it isn't objective? We have the brains to look and see right from wrong, and how it affects us and our society. We can choose whether or not to follow that code.

What is more objective than that? I submit that moral relativism is objective. Our morals may change and evolve with society.

They may quickly shift due to adverse circumstances. That makes them both relative as well as objective. Plus, Christian morality, which is supposedly hard-fast and set in stone (literally) changes as much as any other morality.

That's why we don't see Christian's out stoning people on a regular basis.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.