A couple opf quick comments:
AS for feeding the current world population, a report by John Craven on a recent Countryfile (bbc) prog, stated that we, especially the supermarkets and retailers, waste 4 times as much food as could feed the world adequately every year. I think changes to this would in of itself go a long way to easing the population problem.
As for population per se, a recent BBC Horizon programme with David Attenborough claimed that the world could sustain over twice the current number IF we only had about 2 hectares usage per person. Currently though the Developing world 'exists' on less than 1 (usually about 0.5), Europe about 3-4 and the USA over 5.
A much better and fairer re-distribution of land use to support the current 6.8billion (albeit and rising) would seem to be long overdue.
Population control through contraception must apply to all,- (it would also help against STD's like HIV etc) not just the Developing world alongside changes in land use and food distribution. The 'religious' objections would have to be countered though aswell.
GM Crops are touted, usually by agribusinesses, as a supposed solution, but given my first remarks re the wastage, and the UN report in 2009 that Africa could feed itself on organic crops; that Sth American soils could be rejuvenated by bean crops, then crop-rotated with maize etc, within a few years and without loads of pesticide use (C4 prog in 2003-Julian Pettifer) and that we have bearly started down these routes, this along with, as I said better land usage, and distribution would not require GM.