I think it is not up to me to judge or legislate any ones' reproductive choices.
I have one child, I have friends who have 3 and 4 children. Does that make me more responsible? No. Will their having more children destroy the planet. I don't think so.
In advanced countries the trend is towards less children. Third world countries tend to have more children per family to compensate for higher infant mortality rates and to ensure that parents are taken care of in their old age - the more children you have that survive to adulthood, the more people to help feed you when you are old. We no longer need that system as we have a better economic system with built in retirement programs. Those things don't exist in third world countries.
I look at this way - do we want to be like China? The government enforced a Zero Population Growth policy on its citizens in the 70s limiting each family to only one child. The result was an increase in abortions, and abandonment of female children - as male children are culturally more valued. Rural areas are allowed to have more than one child, with prior approval, as they are needed to work the farms and fields.
My carbon footprint will not destroy the earth. The major producers of pollutants are the very industries that make us a "first" world country. And while the world council is developing emissions standards, many countries, especially those moving from third to first world status, are in the middle of their industrial revolutions and are not abiding by the emissions standards. They cannot while they are struggling to leave their third world economies behind. Currently industries that exceed emission standards simply pay a monetary fine - not much of a deterrent, eh.
I do what I can, keep my water heater on a lower setting, turn off lights when I leave a room, turn off power strips to electronics when not home, try to be more efficient when running errands to burn less fuel, etc.
But, this problem has built up over centuries, and just because, as a country, we may be ahead of the curve, we do not have the right to judge or impose our familial values on others.
Check out http://en.wikipedia.org/wiki/Zero_population_growth
And for another point of view read the works of Thomas Robert Malthus(1766 – 1834)