Population control has been talked about publicly. It was discussed more prevalently in the 1970s -- it just doesn't get talked about much anymore.
Here is a recent video of David Rockefeller speaking about the importance of population control for the UN and other international bodies (such as you mentioned):
Again, it's not so much a conspiracy -- you don't see the establishment giving presentations on who killed JFK at conferences. But as you can see, population control is a discussed in these settings -- just not in the mass media. As explained in "Manufacturing Consent," these type of framed issues are just part of the political economy.