I think the
competitive model for species
evolution and
resource consumption that is applied to all
animals in nature doesn't hold true for humans. After all it is our
dynamically shifting co-operative nature that allows us to form
society, and to support the vast population that we currently have. The simple fact of the matter is that the reason more children are born and survive is because our technology is
capable of supporting them. The tech level won't decrease any time soon, and so we will be able to support further increases to the size of human population without too many difficulties. The fears of overpopulation in the eighties didn't factor in the extreme
efficiency of
food corporations, or the closer ties in the
global economy: both of which make the die backs and other overpopulation issues less likely.
The lack of space issue can be dealt with, well, SPACE. I believe that long before we run out of room and resources here because of a burgeoning population, there will be colonies on the other planets in this system, notably Mars. To give you some idea of how ridiculous this particular argument is, it is worth noting that the entire population of the world (thats right, all 6 billion of us) can fit neatly with standing room on the Isle of Wight. A very very small island of the coast of the UK. I therefore don't believe we will be running out of room soon.
The waste issues can be dealt with by appropriate environmental policies and attached enforcements. People need to learn how to recycle anyway, and if they want their children to live good lives then the incentive is there.
As for the argument that overpopulation would stress the current political and social, and economic systems. I say, bring it on. We need change, and radical change at that, I do not see how the human race can continue to strive with precisely the values it has at the moment, they continue to evolve and we alongside them. The systems will change to accomodate more of us. More of us means more geniuses, more awareness, more civilisation, and more work done on ourselves and our environment.