This is the million-dollar question
where we would be and what we could accomplish were we to simply listen to the lost voice of history that desperately struggles to not have to repeat itself.
I was precisely writing about revenge yesterday (for a different post). It is a dark path and i don't do well in the dark. Why so many people follow that path is beyond me. Disgracefully, political leaders, on behalf of entire nations take this retaliatory attitude and cause death and destruction on a daily basis.
As you rightly point out, violence and hatred begets more of the same, usually at a higher scale.
I aslo posed recenlty a question on musing.io about why is it that we can't get along with each other, what is wrong with humanity (it wasn't much valued and mostly misunderstood). You have answered that question brilliantly here.
It's not that we are so many and so diversed, therefore making understanding impossible (if that is the case, why do we think so highly of ourselves, why do we conceive such ambitious projects of human development and possibilities?).
Either we are great and can therefore overcome differences or we are doomed to disaster and therefore uncapable of conceiving or materializing big dreams. I believe in the former.