Confused about the act of killing

[asmith]

Hello,

This thing has been making me busy. I won't ramble and just cut to the chase.
I think it's safe to say that every creature in the world has evolved/co-evolved to their current state because of the need to survive. A big part of that is related to killing and getting killed. I think we can say if our life wasn't threatened in the first place, we wouldn't have evolved at all.

So basically at the time we could mark ourselves as humans, killing/protecting is a part of our lives. Looking back at human history, I see many cultures/religions are forced by wars.
* Islam is basically spread through war. Muslims have killed/raped loads of people of other countries at the beginning years. Today Muslims of those countries are ignorant of that fact or really don't care, thus mission accomplished.
* India or many African countries were exploited, today they are using their predator's language/culture, mission accomplished.

On the other side, we have many social codes like "killing is bad" which we're grown up with. I could understand that and I say that is the human rule trying to make a better world. But is that all there is to it? Killing a person looks extremely harsh and not "the answer". But looking at our past, it seems like a decent way of life. In other words, we could commit genocide and if we could succeed in keeping ourselves in place for some decades, we could stay there for good.

Please correct me if I'm wrong.
(I'm looking for a technical sense, no religious answers please.)

[JackBean]

I'm not sure what you want to hear. That if we killed someone it will be fine because that's our nature?

[asmith]

Well I'm just confused. Not that I want to kill people. Some day ago I saw a dead cat on the street and I was about to cry.

I just don't get this. Our human culture, what it is today, seems to be based on genocides. It's like "ok we attack and massacre other people but when we settled we'll be good after". It seems it has worked fine.

I think somehow I'd like hear I'm being naive and not considering various points.