Voluntary cooperation is natural. It happens all the time in the animal world, and it happens all the time with humans.
"as Darwin suggests -- through "the war of all against all."
You mean as Hobbes said. As I already posted, Hobbes is the originator of this phrase. It is the basis of his Leviathan, and was well known by political theorists in the 19th century. Also, when Marx used it, he was describing capitalism, not how things would be under communism. Lastly, the fact that there is a severe struggle within nature for survival is a true statement. The fact that Darwin quoted this (from De Condolle, who got it from Hobbes) only means he was describing biological reality. Do you disagree that there is a severe struggle for existence in nature?
Yes, I do disagree. It seems to me that the gift of life is perfectly gratuitous. And is made as perfect as mortal things can be made, through a process of cooperation, not via struggle or conflict.
But then, I am not a materialist, physicalist, atheist, or reductionist monist in basic persuasion. So go figure. And try to have some fun while you're doing that.