Isn’t it presumptuous for wealthier parts of the world to advise poor countries to stabilize or even reduce their populations?

Wealthier countries can afford to gather and analyze information on the impact of population growth, including in the Third World.  This analysis shows that humanity is rapidly undermining the ability of the earth to sustain even current population levels.  It is the major reason countries are failing to achieve reasonable economic well-being.  It would be irresponsible not to share this information with others who need and could most benefit from it.  Ultimately, however, each country must decide for itself if and how this information is used to shape public policies.