Originally Posted by 
tact
				
			 
			No, am not coming from an economics perspective, though of course that does come along for the ride.    My thinking is purely in relation to the number of beings that the closed system that we live on, the earth, can sustain.   
My point was that so many schemes to address this focus only on limiting new entrants to life's journey (i.e. births overall, or population movements to a life in a specific country).   A fully rounded picture would also deal with culling the old codgers constantly, trimming the tree so to speak, to make room for continuous well planned new growth. 
To keep the population (of the globe, or of a specific country) at a relatively constant number that is sustainable, could be managed by simply controlling the birth rate etc....      But why not have a more proactive system in play, active culling at a certain age?   This allows for better planning around the introduction of new lives to the fixed size pool.   Mitigates the risks of increasing lifespans.   Ensures constant fresh blood.
The actual number of codgers to be culled may need to be adjusted seasonally -   To account for surprise departures through natural disasters, birth defects, suicides, etc.   Given the lead time to commissioning new life entrants (9mths), any unexpected life terminations could result in an extension of time for some lucky old codgers.   (How to administer that is open for discussion).    ;)