"So if I decide I want to abide by the brutal side of nature?"
You would not get the chance to repeat that behavior. Humans have decided that such behavior is not permissible (based on evolutionarily optimized standards of what constitutes acceptable behavior)
Still, you haven't established that such ethics are the standard of the universe (which is all that exists, remember). You want to believe that the field of human ethics is the product of an evolutionary process for "optimization," and that human beings decide what is best! In truth, all you're really saying is that majority rule decides what right and wrong is, which is completely arbitrary. If you're going to look to evolutionary theory as your ground for proper behavior, the kind of behavior that best insures our survival, the numbers are not on your side.
Look Zombie, human beings are johnny-come-lately's to this planet. The jury is still out on whether superior intelligence is the best adaptation for survival. Man has only been around a few million years, and modern man (with his superior intelligence and "optimized ethics") has been around only about 10,000 years. And the prospects of our survival are not looking too good. The way we're going, it doesn't look like modern man can last too much longer.
The dinosaurs, on the other hand, ruled this planet for nearly 200 million years, and I doubt seriously their inferior intelligence developed anything that we could call "optimized ethics." Truth be told, the numbers are much better for inferior intelligence being most adept for survival.
Point? If "ethics" are really drawn from nature's evolutionary processes, there is really no compelling reason to abide by such. If nature is all there is, then the dinosaurs got it right! Huff and puff all you like, but there's no reason to believe that "optimized ethics" is really the best adaptation for survival.
You should add to that list several millennia worth of religiously-inspired genocide. Only in the last hundred years of recorded history have we seen genocide not exclusively motivated by religion. Much tyranny in the 20th century was still religiously motivated, however.
The "religion is genocide" argument is bogus. At the root of most of what you call "religious genocide" is a struggle for territory or self determination. The present strife in Northern Ireland, for example is not about transubstantiation of votive candles, but self determination. The last century's destruction of human life came not from religion, but political ideology. Indeed, Hitler, Stalin, Mao, Pol Pot...etc., persecuted religion (mainly Christianity and Judaism), and murdered over 100 million people.
You have a point... we do still cling to the same asinine beliefs as those ancient civilizations at the beginning of history. Slavery, racism, subjugation of women, superstition... all are divisive relics of our tribal past.
See point on dinosaurs above! The potential for nuclear holocaust did not exist in our tribal past. The smarter we get, the closer we get to destroying ourselves. Knowledge appears more and more to be inimical to survival. If survival, via reproducibility, is what drives the evolutionary process, then intelligence does not appear to be the best adaptation for survival. So it's probably best that we go back to tribalism, or maybe even the law of the jungle? If nature is our guide...if nature is all there is, then the evidence is on my side!