Problem of good and evil for an atheist

[chasm]

So what is one example of something absolutely evil?
Killing a baby, an innocent baby for any reason is evil. (please dont derail this thread with attacking the Bible)

If you think killing a baby is ever justified, I think it is safe to say, that you are sick and perveted.

Some cultures did practice killing babies, however, we would call them 'immoral'.

I guess God is immoral, too, since he killed innocent babies.

God gives Joshua the city of Jericho. All, including babies, are killed with swords, and the city is dedicated to the Lord. JOSHUA 6:21-27

There is no natural explanation for the concept of good and evil. So where did it come from?

From evolution. From our instinct to preserve our species and the planet we live on. From us, our minds. We made it up. Besides, good and evil are very subjective terms.

I personally think it came from a cosmological battle between good and evil, although I cant conclude and prove that it, it explains things much better than anything else.

A... what? You mean, like, there's a bunch of superheroes and villains fighting somewhere in the universe RIGHT NOW?

P.S. Watch this:
http://www.youtube.com/watch?v=hCovYF51qHE