I am not interested in declaring anything haram or halal ....... it's given in Quran. No man should be taking it upon himself to declare anything haram or halal for others outside the Quran, else what is so different between a donkey and a camel?
On this topic of overpopulation I have stated multiple times on this forum that the Quranic verse presented in defense of 'keep producing because ALLAH is the provider' is totally misunderstood and everyone needs to read it carefully again and again till the time they get to understand the actual message. The crux of the matter is most people think preventing a sperm from fertilizing an egg is equivalent to killing a child ... well if that is the truth .... then how do you explain a sterile, barren couple trying for a baby again and again and failing at it? That would mean killing millions of babies in the process? Or just take the simple example, it takes one sperm out of million to fertilize an egg .... what about the rest of the millions or thousands or whatever? Are those babies sacrificed for making one baby? Or how about million babies killed in a wet dream? .... ask yourself does it make any sense?
The killing in Quran doesn't only mean to murder someone, it also means to dehumanize someone, to make them live like helpless poor orphans for all their life, make them live in state of hell forever on this Earth, deprive them of the resources and means to develop into healthy prosperous human beings.
"Don't kill your children" ....... your children, I don't know how this extends to a sperm and an egg, but for me its very clear, raise your children healthy, provide for them out of what ALLAH has bestowed upon us in this Earth, help them grow to their fullest. A child needs parents for his initial years for his survival and those years shape his future. Don't deprive them of healthy diet, education and all that is necessary for their development into healthy humans. And this message is not for an individual its for the State, for the society. A person producing 12 kids is actually not only depriving his children, but someones else's as well. Remember no "mun o salwa" is going to descend from Heavens, all means and resources are already provided for in this Earth. With scarce resources and means of production, there should be equality in everything including the number of children a family gets to produce.
Having said this, Quran is also very clear on what should be the purpose of a married couple having sex. That verse is what needs to be consulted before opting any measure of preventing pregnancy. Pure lust is a very negative motive ....... not encouraged, nor desired. So? in an utopia where Quran's principles are fully implemented, Muslims would refrain from any sexual activity in our given situation ...... but we don't live in utopia. So everyone (the ones who have a brain) should decide for themselves how they wish to remain within limits without bringing any harm to society. That (refraining from any sexual activity) is the situation where "Sabar" patience is practiced ....... producing twenty kids and then not having enough to feed them is not sabar but a curse.