There is one big problem with the concept of self impossed limits on kids... A great example of this issue can be seen in France today. The more 'enlightened' people are quickly fading away (population wise) and the amount of foreigners (mostly muslim) are taking over. Basically, unless you can enforce it globally, all your're really doing is allowing your 'kind' (those who agree with limitting the amount of kids they have and other environmentally friendly life choices) to be replaced at a faster rate by those who could care less beyond what happens today.