So in your fantasy world we would be at 8.5 billion people along with low poverty, hunger, and deaths from war... but replacing capitalism with socialism.
Likely you fantasize no income and instead it would be the whole "From each according to his ability, to each according to his needs" thing, right?
Unfortunately for your fantasy... the result of socialism has always been the deaths of millions of people through starvation and murder (followed by collapse and/or acceptance of capitalism)