This is in my humble opinion a noble and misguided conclusion.
Since there is no moral way to control the populations of other peoples who are lacking in environmental consciousness, they would continue to grow. Whereas environmentally conscious populations would remain near-static, relatively. The only thing such a plan would accomplish is breeding environmental consciousness out of the human race.
This is something that happens often as wealth is achieved on an individual or national level. Rich people develop tastes for luxuries, and children are expensive to raise in similar levels of luxury. This causes children to be seen as a threat to such luxurious lifestyles to which the prospective parents have grown accustomed. Consequently parents of some luxury are less likely to have children than poor people whose own lifestyle is more meager. In essence the rich, in their unconscious selfishness often breed themselves out of a darwinistic existence. Unenlightened greed is not a survival trait, it's more often a mortal flaw.
A more environment conscious mindset in which people forego their own comfort in favor of a flourishing environment alongside a flourishing society will strengthen and invigorate individuals and societies. A healthier, stronger, disciplined, devoted people have more survivability than those who fumble around childishly polluting their own environments. This way ensures that the healthier society forces the less healthy society out of existence. Instead of the healthier society commiting suicide, as suggested above. | 
