Religion is one of the most human concepts. So is killing. Of course one has invaded the other.
Where we should be working is to carve out the part of us that can't help but kill people whose ideals we don't like. I find it pretty naive the idea that if we just all accept a mushy liberalism, the killing will stop. Even more ridiculous to me is the New Atheist idea that if we all just learn about Science, there will be centuries of peace.
Long story short, we can, theoretically, promote a particular way of life and even verbally condemn those who wont accept it without killing them. I doubt that we'll ever get there, but I just always feel like patting the "imagine, no religion" types on the head.